Gas/Propane Basics Archives | Page 2 of 3

Part 9, from the Nov/Dec 2022 Indoor Comfort

Parts 1 & 2, from the Jul/Aug and Sep/Oct 2021 Indoor Comfort can be found here.

Part 3, from the Nov/Dec 2021 Indoor Comfort can be found here.

Part 4, from the Jan/Feb 2022 Indoor Comfort can be found here.

Part 5, from the Mar/Apr 2022 Indoor Comfort can be found here.

Part 6, from the May/Jun 2022 Indoor Comfort can be found here.

Part 7, from the Jul/Aug 2022 Indoor Comfort can be found here.

Part 8, from the Sep/Oct 2022 Indoor Comfort can be found here.

It doesn’t matter if it is a forced warm air furnace or a forced hot water boiler—the same basic system is used to perform safe ignition followed by consistent operation throughout the entire call for heat.

There are, however, different ways the system is applied from intermittent pilot application to direct spark ignition and including hot surface ignition (HSI). Each has its own distinct advantages and problems. We’ll now attempt to resolve those burner problems related to these systems, as well as offer corrections and diagnostics.

We will start with the basics and then continue to operation, typical problems, diagnosis, troubleshooting procedures and a final solution to a particular problem. It’s easy to jump to conclusions with these systems and just change parts to hopefully solve a problem. That is, however, time-consuming and costly.

I invite you to visit our new Facebook page. I look forward to seeing you there.

We are presently doing a series on Honeywell SmartValve; in this article, we will cover SmartValve Third Generation and walk you through the step-by-step process of operation with these controls.

SV9510/SV9520 Sequence of Operation
Figure 1 is the sequence of operation for SV9510 and SV9520 SmartValve. The various diagrams featured in this article will show you the circuits involved.

Referring to Figure 1 and Figure 2 for the Sequence of Operation and to Figure 3 for a diagram, let’s go through the Sequence of Operation.

When power to both 120 VAC and 24 VAC is applied to the system, the LED on the SmartValve will be pulsing “in the Heartbeat mode”—bright-dim-bright-dim, etc. L1 (Hot) is fed to L1 on the EFT. Then 120 VAC is fed from XFMR (transformer) to an external 40 VA or 50 VA transformers, depending on which valve. From the transformer, 24 VAC is fed to the 24VAC/Com terminals on the EFT.

The dotted lines in Figure 3 are my additions to illustrate the printed circuit board feed from L1 to P1-1 120 VAC, and from neutral to P1-4, as well as the 24 VAC (Hot) from terminal 24VAC to P1-6 and the common (COM) to P1-3. The ST9160 Electronic Fan Timer will be covered in a later section.

The setup for this wiring shown in Figure 3 has the 120 VAC to the SmartValve interrupted and 24 VAC is fed direct on the “R” wire to C1-7 and the “C” to C1-6 on the SmartValve. On a call for heat, a circuit is completed through R and W on the ST9160 the air-proving switch, which must then prove open in 30 seconds. If it does, then 120 VAC is fed from P1-1 to C3-2 and back on neutral from C3-4 to P1-4. Then 120 VAC is fed from C3-1 to the Combustion Air Blower and back to neutral on C3-3. Then the prepurge begins.

At the end of the prepurge, the HSI warm-up starts. The igniter warm-up time for the Norton 271 (used with SV9510) is 17 seconds on the first try and 27 seconds on subsequent tries. The Norton 601 (used with SV9520) warm-up is five seconds on the first try and then 10 seconds on subsequent tries.

The main valve opens and ignition takes place. The flame rod proves the burner flame and the DATA signal is fed from C1-4 to P1-2 to start the fan-on time sequence. The fan will usually come on in 30 to 60 seconds.

When the call for heat ends, and R and W breaks, power to the Combustion Air Blower ceases after post-purge. The air proving switch opens and the DATA signal ceases; the Electronic Fan Timer goes to the dip switch set fan-off run time. At the end of that time, everything is ready for the next call for heat.

Figure 4 shows how the 208907 terminal board allows compatibility with power-stealing thermostats. Many of the control boards cannot be used with power-stealing thermostats unless there is an isolating relay used or a 100 ohm 10 watt resistor placed across W and C.

Figure 5 shows a typical wiring diagram with a Forced Hot Water System using a R8285D Honeywell Control Center. With this setup, the 120 VAC is fed direct from the junction box to C3-2 (Hot)/C3-4 (Neutral); in this case, the 24 VAC is interrupted.

L1 Hot is also fed to Pin 3 on the R8285; also, 24 VAC is fed to Pin 4. On a call for heat from the thermostat, 24 VAC is fed from “R” through the thermostat to “G,” then to the relay coil and back to “C.” This brings in the two sets of relay contacts—1–3 sends 120 VAC to the circulator; 4–6 takes 24 VAC from “R” to “Y” through the aquastat control (high limit) to the R and DATA wire C1-7 and C1-4 (DATA). The sequence after that is the same as the sequence for Figure 3.

Figure 6 is an example of wiring direct to the thermostat. This setup could also be used for a steam system by adding a Low Water Cut-Off and Pressuretrol in place of the limit switch.
The 24 VAC is again interrupted and the 120 VAC is fed direct to C3-2 and C3-4. In many instances, a jumper from C1-4 to C1-7 may accomplish the wiring from the DATA to “R” wire. Pay particular attention to the triangle notes 1–6 in Figure 6.

In the next article we will discuss troubleshooting the SmartValve Third Generation. ICM

Part 8, from the Sep/Oct 2022 Indoor Comfort

Parts 1 & 2, from the Jul/Aug and Sep/Oct 2021 Indoor Comfort can be found here.

Part 3, from the Nov/Dec 2021 Indoor Comfort can be found here.

Part 4, from the Jan/Feb 2022 Indoor Comfort can be found here.

Part 5, from the Mar/Apr 2022 Indoor Comfort can be found here.

Part 6, from the May/Jun 2022 Indoor Comfort can be found here.

Part 7, from the Jul/Aug 2022 Indoor Comfort can be found here.

I invite you to visit our new Facebook page Timmie’s Tips on Gas. I look forward to seeing you there.

We are presently doing a series on Honeywell Smart Valve™. We will pick up where we left off in the last article and cover Smart Valve™ The Third Generation. We will walk you through the step-by-step process of operation with these controls.

SmartValve™ Third Generation
The third generation of SmartValve™ became available to the original equipment manufacturers (OEMs) in late 1998/early 1999. It includes the SV9510/SV9520 and SV9610/SV9620.

The SmartValve™ works in conjunction with the Honeywell Electronic Fan Timer ST9160. It uses direct burner ignition line voltage igniters, such as the Norton 271, which has been used on HSI for many years. The new igniter used is the Norton 601.

The SV9540/SV9640 is also used with the EFT ST9160 control. It uses the same 24-volt igniter system used on SmartValve™ Generation I and II.

There is also a SmartValve™ SV9540Q used with Electronic Fan Time ST9162. This is a two-stage system that will be covered in a later discussion.

SV9510/SV9520; SV9610/SV9620 SmartValve™ System Controls
Application
The SV9510/SV9520 and SV9610/SV9620 SmartValve™ System Controls combine gas flow control and electronic direct main burner ignition sequencing functions into a single unit. The ignition source is a 120V HSI lighting the main burner flame. Two types of 120V igniters may be used, as seen in Table 1.

The control provides all gas ignition safety functions by controlling gas flow, ignition source and a 120 VAC combustion air blower. The control also monitors the appliance airflow-proving switch and limit string to assure proper appliance operation.

The SmartValve™ System Controls provide pre-purge, post-purge and timed trial for ignition with multiple ignition trials and auto reset from lockout. Diagnostic LED indicates system status.

The control communicates directly with the ST9160 Electronic Fan Timer (EFT) in typical forced warm air furnace applications. It will also interface with the 208907 Terminal Board, providing compatibility with power-stealing thermostats. Alternately, it directly interfaces with the appropriate power supplies and a system thermostat for additional appliance applications. When controlled directly by a thermostat, the control does not provide a post-purge function, as power to the control is removed when the thermostat’s call for heat ends.

This system is suitable for a wide range of fan-assisted, combustion, gas-fired appliances including furnaces, rooftop furnaces, boilers, unit heaters, infrared heaters, water heaters and commercial cooking appliances.

The specific application of the SmartValve™ System is the responsibility of the appliance manufacturer. See Table 2 for temperature ranges and regulator types.

Line voltage polarity sensing models monitor the line voltage input connection to assure line voltage polarity is correct. If line voltage polarity is incorrect, the LED diagnosis code will flash and the control will not respond to the call for heat. These models also provide added LED diagnostic codes (“6+”) to indicate the reason the control has moved to the lockout state.

Depending on models, various timings are available, such as 15 or 30 seconds pre-purge; post-purge five seconds (typical depending on model; this is not available when the SmartValve™ is connected directly to the thermostat); five, seven or nine seconds trial for ignition; 60-minute soft lockout; three retries; four trials before lockout. The other unusual feature is that the draft inducer is now controlled from the SmartValve™; depending on the version, this is accomplished by either interrupting the 120 volts or 24-volt signal. This will be defined as each diagram is discussed.

The capacities on SV9510, 20 and 40½” x ½” 200,000 BTUs maximum and on the SV9610, 20, 40¾” x ¾” is 415,000 BTUs.

Figure 1 is an illustration of the top view of the valves. The C3 connector is for 120-volt power, and this is also the feed for the draft inducer. The C2 connector is for the 120-volt HSI, either the Norton 271 Silicon Carbide in the case of the SV9510, or the Norton 601 120 volt Silicon Nitride Igniter used only with the SV9520 model. The C1 connector is the low voltage 24-volt AC hookup.

The designation of pin numbers for the C1 and C3 connectors on the SmartValve™ and the 6-pin connector on the ST9160 Electronic Fan Timer are illustrated in Figure 2.

Converting Ignition System Control
From Natural Gas to LP Gas Application (or LP Gas to Natural Gas Application)
Always change the main burner orifices as provided by the manufacturer of the equipment being converted. Ignition system controls are factory-set for natural (and manufactured) or LP gas. Do not attempt to use an ignition system control set for natural (manufactured) gas on LP gas, or an ignition system control set for LP gas on natural (manufactured) gas.

Ignition system controls with standard or slow opening regulators (SV9510M, H/ SV9520M, H, K) can be converted from one gas to the other with a conversion kit (ordered separately). Order part No. 393691 to convert from natural (manufactured) to LP gas; order part No. 394588 to convert from LP to natural (manufactured) gas.

Two-stage ignition system controls (those with N and Q suffix letters) can be converted using a conversion kit (ordered separately). Order part No. 396021 to convert from natural (manufactured) to LP gas; order part No. 396025 to convert from LP to natural (manufactured) gas.

IMPORTANT: Ignition system controls with step-opening regulators (SV9510P/ SV9520P) cannot be field-converted to LP or natural gas. See Table 3 for pressure settings for valves.

SV9510/SV9520 Sequence of Operation
Figure 3 is the sequence of operation for the SV9510 and SV9520 SmartValve™.

Training
Finally, I love to teach and would love to have you come and join us for some training. We also conduct seminars on the following topics and many others:

Five-Day Course
• Fundamentals of Gas
• Circuitry & Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems

One-Day Course
• Powerpile Systems

Three-Day Course
• Combustion Testing Design Gas Equipment
• Conversion Burners

Four-Day Course Designed for Your Specific Need
• Modulating/Condensing Boilers

For more information, call 401-437-0557 or write to:
Gas Appliance Service Training & Consulting
42 Village Drive, Riverside, RI 02915.
E-mail: timmcelwain@gastcri.com. ICM

Part 7, from the Jul/Aug 2022 Indoor Comfort

Parts 1 & 2, from the Jul/Aug and Sep/Oct 2021 Indoor Comfort can be found here.

Part 3, from the Nov/Dec 2021 Indoor Comfort can be found here.

Part 4, from the Jan/Feb 2022 Indoor Comfort can be found here.

Part 5, from the Mar/Apr 2022 Indoor Comfort can be found here.

Part 6, from the May/Jun 2022 Indoor Comfort can be found here.

There are, however, different ways the system is applied from intermittent pilot application to direct spark ignition and including hot surface ignition. Each has its own distinct advantages and problems. We’ll now attempt to resolve those burner problems related to these systems, as well as offer corrections and diagnostics.

I invite you to visit our new Facebook page Timmie’s Tips on Gas. I look forward to seeing you there.

Forced hot water boiler wiring diagram
I want to emphasize once again how important knowing the sequence of operation of equipment is to proper diagnosis of problems. We are now going to go over sequence of operation on a forced hot water system. In the last article we covered forced warm air.

The system shown in Figure 2 is using a control center (transformer and relay) shown in Figure 1. The same control, when used on a forced warm air system, is called a “fan control center.” It is important to note that the wiring is different for a boiler versus a furnace. The use of a control center on a warm air furnace or boiler is a convenient place to connect wires and also makes for easier troubleshooting.

The transformer has the wiring connections attached. The “R” and “C” terminals are the only actual voltage connections. The other terminals are for wiring connections. The relay part of the control center is field replaceable. The best thing is to carry a SPDT relay, which can be used to replace another SPDT or SPST relay without any wiring changes in the junction box. Being able to stay out of the junction box is very important as the possibilities of connections coming loose are increased when you have to get into the “J” Box.

In addition to the “control center,” we have a Generation I SmartValve™ and a Honeywell D-892 vent damper. In Figure 2, the vent damper is shown with only the external wiring connections. It is sometimes difficult to imagine what is going on inside a control if the internal connections and components are not shown. I find that showing the internal operation of controls makes following the electrical path easier.

In Figure 3, we show the internal connections of the D892 vent damper. The sequence of operation we are going to follow is best understood using Figure 3. The purpose of the vent damper is to increase the efficiency of the equipment a little more by shutting down the standby loss from the boiler during the time when the thermostat is not calling. Anytime a vent damper is used, it must have an interlock circuit to ensure that the unit does not fire with the damper closed. This particular damper from Honeywell is powered closed and must have a continuous uninterrupted 24 volts at all times. When a call for heat takes place, the motor in the damper is de-energized and it will spring open. This, in turn, will activate the two N.O. sides of the switches (end switches).

In addition to power being required to the vent damper on a continuous basis, the SmartValve™ must also have an uninterrupted 24 volts at all times. When the SmartValve™ is used on a boiler application, the Electronic Fan Timer (EFT) output from the SmartValve™ is not used. The EFT output is only needed with a furnace.

Sequence of operation
The sequence of operation with this example is as follows:
1. Uninterrupted 24 VAC from R/C on Control Center is fed to SmartValve™.
2. 24 VAC to terminal 1 on the vent damper through the orange wire, through the right-hand side of relay Kl (closed) the NC set of S3 contacts to T2 through the motor to T1 and returning back to terminal 4 on the yellow wire. This powers the motor and damper is closed.
3. On a call for heat, the coil in the control center is powered and two sets of contacts close.
a. The left-hand set takes 120 VAC from L1 to Circulator Pump and back to L2.
b. The other set takes 24 VAC from R through spill switch, rollout switch and aquastat to terminal 2 on the vent damper.
4. The 24 VAC on 2 (black wire) goes to energize relay K1 in vent damper actuator and back to 4 on the yellow wire, the right-hand K1 switch is opened breaking power to the damper motor K1 switch now makes the left-hand side. The motor is now de-energized and the spring now opens the vent damper (mechanical action); the two normally open (N.O.) contacts close S1 and S2.
5. The relay stays powered through terminal 2 (black wire) during the entire call for heat unless one of the safeties opens.
6. The S1 and S2 (SPDT) set are in series and when the motor de-energizes and the spring opens the damper, they provide the path for 24 VAC through the left-hand side of K1 through S1 and S2 on the blue wire terminal to 3 on the damper powering the SmartValve™.
7. Now 24 VAC is fed out of terminal 3 on the vent damper to the interrupted leg of SmartValve™. The burner is now on.
8. When the call for heat ends, the control center relay coil is de-energized, as is also the K1 relay coil and the circulator shuts down. When K1 is de-energized, the K1 relay switches back to the right-hand side and the motor is powered closed. End switch contacts S1 and S2 are now tripped back to NC position.
9. Power is shut off to the interrupted leg of SmartValve™ and the burner shuts down.
It should be noted that switch S3 stays NC at all times unless the service switch is tripped; in that case it will de-energize the motor and the damper will now open manually.

The resistor R1 is to prevent power stealing programmable thermostats from energizing the damper when there is no call for heat. This is one of the phenomena of some power-stealing-type thermostats. ICM

Part VI, from the May/Jun 2022 Indoor Comfort

Parts I & II, from the Jul/Aug and Sep/Oct 2021 Indoor Comfort can be found here.

Part III, from the Nov/Dec 2021 Indoor Comfort can be found here.

Part IV, from the Jan/Feb 2022 Indoor Comfort can be found here.

Part V, from the Mar/Apr 2022 Indoor Comfort can be found here.

I invite you to visit our new Facebook page Timmie’s Tips on Gas, I look forward to seeing you there

We are presently doing a series on Honeywell SmartValve™. In this article, we will cover the Smart-Valve™ being used in a Forced Warm Air System. The next article will cover SmartValve™ with a Forced Hot Water System.

Troubleshooting electronic system
There are many different systems in use today on both Forced Warm Air and Forced Hot Water Systems. Knowing how to diagnose and troubleshoot these systems is something everyone needs to be able to do. There are some basic steps to follow.

Figure 1 is a basic diagram of a SmartValve™ hookup; we will be going much deeper into the process of diagnoses than this diagram will allow.

One of the first things to know in order to properly troubleshoot a system is the sequence of operation. If you do not know how it is supposed to work, then how will you be able to fix it? In this segment we are going to look at a Forced Warm Air System.

This particular system is composed of a Honeywell SmartValve™ Generation I SV9500/9600 with a Honeywell Electronic Fan Timer ST9120A, B or C. Using the diagram shown in Figure 2 we will walk through a sequence of operation on this system.

It is interesting to note that modern systems all come with wiring diagrams, both connection diagrams and ladder diagrams, trouble trees, and in some cases we even have diagnostic LEDs to help us find the problems. These, along with a written-out sequence of operation, should make our jobs easier.

The diagram shown in Figure 2 is for a Forced Warm Air System; it shows some air conditioning components, which will not be covered in this instruction.

Sequence of operation
The sequence of operation is as follows:

1. There is 120 VAC fed to terminal S1 on EFT—Neutral wire to N1.

2. 120 VAC is fed from terminal S2 to the primary of a 24 VAC transformer—N4 is neutral. In order to be able to more easily follow this sequence, Figure 3 will illustrate pin numbers and shape of pins for the ST9120.

3. The secondary of transformer goes to X (hot) C (common) Note: on some EFTs, there is a feed from X–4 and C–2 on 6-pin connector.

4. There is an un-interrupted 24 VAC from X and C to SmartValve™ or from pin 4–24 V AC (Hot) to Pin 2–24VAC (common).

5. When thermostat calls for heat R to W
a. 120 VAC is fed out of DI (draft inducer) to combustion blower neutral to N3.
b. The combustion air blower will cause the pressure switch to make COM to NO.
c. 24 VAC out from X to Pin 1 on 6-pin connector.
d. Pin 1 through limit and roll out switch to pin 6 to R (thermostat) through printed circuit board.
e. R to thermostat back to W to pin 3 on 6-pin connector.
f. Pin 3 to pressure switch and auxiliary limit to thermostat terminal on SmartValve™.

6. SmartValve™ is powered 24 VAC to the igniter, igniter glows and lights pilot gas—pilot proves back on clear (or sometimes black) wire a .3 microamp signal or greater. The main valve opens and lights from pilot burner. At this time, a data signal is superimposed on a voltage signal and fed to the EFT pin 5 on 6-pin connector.

7. Different ST9120 EFT boards will have dip switches for fan delay on and fan delay off (three dip switches) or just fan off delay (two dip switches). The 2-dip switch model has a fixed fan on time of 30 seconds. The 3-dip switch model has fan on times of 30 or 60 seconds. The off time on both can be 60, 100, 140 or 180 seconds. The data signal back to the EFT will trigger the fan on timing.

8. The fan comes on and runs until the thermostat is satisfied. Depending on the connection at the motor the fan will run on low, medium low, medium high or high speed. For heating, the HEAT terminal on EFT should be connected to low on motor and back to N2 on EFT. (Note: M1 and M2 on EFT are for unused motor leads).

9. When the thermostat is satisfied, the circuit to EFT is broken, the SmartValve™ shuts down and the fan-off delay starts (based on dip switch settings).

10. Fan shuts off—waiting for next call for heat. This completes the sequence of operation. It is the first step in troubleshooting and must be understood in order to further grasp how the system operates.

Figure 4 shows how the sequence takes place coming off the ST9120 control. It should be noted that the Auxiliary Limit is often difficult to find on Forced Warm Air Systems. It is sometimes located on the outlet side of the unit. Its purpose is to protect the heat exchanger from becoming damaged by excessive temperature. The whole idea of higher efficiency systems is to hold as much heat in the unit versus losing heat up the vent. This is why the system fan has to come on so soon.

Educational opportunities
Finally, I love to teach and would love to have you join us for some training. We conduct seminars on the following topics and many others:

One-Day Course:
• Powerpile Systems

Three-Day Course:
• Combustion Testing Design Gas Equipment
• Conversion Burners

Four-Day Course Designed for Your Specific Need:
• Modulating/Condensing Boilers

Five-Day Course:
• Fundamentals of Gas
• Circuitry & Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems

For more information, Tel: 401-437-0557; E-mail: timmcelwain@gastcri.com or write to: Gas Appliance Service Training & Consulting, 42 Village Dr., Riverside, RI 02915. ICM

Part V, from the Mar/Apr 2022 Indoor Comfort

Parts I & II, from the Jul/Aug and Sep/Oct 2021 Indoor Comfort can be found here.

Part III, from the Nov/Dec 2021 Indoor Comfort can be found here.

Part IV, from the Jan/Feb 2022 Indoor Comfort can be found here.

I invite you to visit our new Facebook page Timmie’s Tips on Gas. I look forward to seeing you there.

This article covers some of the tools and aids available to troubleshoot SmartValve™ Generation I and II. Most of these aids can be purchased at your local heating supply stores with the part numbers mentioned here.

SmartValve™ Input Voltage Test Harness (Part # 396085)
The 396085 SmartValve™ Input Voltage Test Harness shown in Figure 1 helps a user to confirm proper appliance control string operation in the field. When installed between the appliance harness and the SmartValve™, the 396085 Test Harness is used to connect a voltmeter to the SmartValve™. This allows the user to monitor the input signals to the SmartValve™ controls. Proper SmartValve™ operation requires the appliance control string to supply the needed input signals during a call for heat.

Test Procedure
Note: Leave SmartValve™ switch in ON position.
1. Turn off gas supply at the appliance shut-off valve.
2. Make sure appliance is powered.
3. Lower the temperature controller setting to make sure there is no call for heat.
4. Disconnect the appliance wiring harness (2×2 connector) from the SmartValve™.
5. Connect the test harness between the appliance wiring and the SmartValve™, as shown in Figure 1. Make sure the keyed connectors lock into place.
6. Measure the voltage between the 24-volt hot (white label) lead and the 24-volt common (gray label) lead on the test harness. If the voltage is less than 20 volts or more than 28 volts, check the appliance power supply and the system transformer for proper functioning. Note: If an appliance is wired so the 24-volt hot lead is controlled with the 24-volt TSTAT/ PSWITCH (yellow label) lead, there is no voltage between the 24-volt hot lead and the 24-volt common lead in Step 6.

7. Disconnect the voltmeter or multimeter from the 24-volt hot lead.
8. Connect the voltmeter or multimeter to the 24-volt TSTAT/PSWITCH (yellow label) lead.
9. Set the temperature controller so it calls for heat.
10. Make sure the meter displays nominal 24 volts while the light-off sequence progresses, and the reading is steady with the element glowing. Note: Thevoltage in Steps 10 and 11 should be between 19 VAC and 26 VAC with the Q3450 element glowing and the gas turned off. If the measured voltage is outside the acceptable range, analyze the appliance control string, input voltage supply and the transformer to identify the problem. Correct the problem and retest the appliance.
11. If the voltage is within the acceptable range, turn off the call for heat and make sure the measured voltage decreases to zero.

12. Disconnect the voltmeter or multimeter leads from the test harness.
13. Connect the leads to the EFT output (green label) lead and the 24-volt common lead.
14. Turn on the gas supply.
15. Initiate a new call for heat.
16. When the appliance main burner lights, measure the voltage between the EFT output lead and the 24-volt common lead. This is a logic signal and can range from 15 VAC through 28 VAC.
17. Test is complete. Turn off appliance call for heat.
18. Disconnect the test harness from the SmartValve™.
19. Connect the appliance wiring harness to the SmartValve™.
20. Turn on call for heat and make sure the appliance works properly.

Measuring SmartValve™ System Flame Current (Part # 395466)
This Honeywell SmartValve™ System flame current kitallows the trained service technician to determine flame current levels generated in a SmartValve™ System equipped gas-fired appliance. Knowing the strength and stability of the flame current signal being generated by the appliance can help the technician diagnose intermittent appliance operation and predict future appliance problems.

Many factors influence the flame current being generated by an installed appliance. The ignition control generates an AC voltage potential between the flame sense rod and the burner ground area. When flame is present, the geometry of the flame rod/ground area (1–4) combines with the voltage potential present to generate a low-level (microamperes) rectified DC current. The ignition control monitors this current to determine if sufficient flame is present to operate the appliance. If the appliance does not generate sufficient flame current, the main burner will not operate and the appliance will not deliver heat. If the flame current generated is unstable and fluctuates, there is high likelihood for inconsistent appliance operation. The service technician must insure that the appliance generates a strong and steady flame current well above the minimum threshold to assure reliable appliance operation.

Honeywell SmartValve™ Systems are available with two types of ignition sequences:

• Intermittent pilot models use a low voltage hot surface ignition (HSI) element to light the pilot gas; main burner gas flows and the main burner lights when the pilot flame is sensed.

• Direct hot surface ignition models use a 120-volt hot surface ignition element to directly light main burner gas; if the main flame is sensed at the end of the trial for ignition, the main burner continues to fire.

The kit shown in Figure 2a and Figure 2b is suitable to measure flame current on both types of systems. Select the proper procedure, below, based on the type of SmartValve™ System in the appliance. Equipment needed:

1. Analog DC microammeter, such as Honeywell W136, which has a 0 to 25 microampere range, or
2. Digital volt-ohmmeter with a DC millivolt scale

Measuring Pilot Burner Flame Current On Intermittent Pilot SmartValve™ Systems

Intermittent Pilot SmartValve™ Systems include: SV9401, SV9402, SV9403, SV9501, SV9502, SV9503, SV9601, SV9602, SV9440, SV9450, SV9541 and SV9640.

When testing with this kit in Figures 2a and 2b:

1. Read these instructions carefully. Failure to follow the instructions can damage the product or cause hazardous conditions.
2. Check the ratings given in the instructions and on the product to make sure the product is suitable for your application.
3. Troubleshooter must be a trained, experienced service technician.
4. After completing the measurements, use the appliance instructions to check the product operation.

IMPORTANT: Accurate flame current measurement can be performed only with the pilot flame lit and the main flame not lit. When measuring with this kit, the appliance main burner orifices should be temporarily plugged while measuring system flame current. Be sure to remove the temporary plug and check the appliance for proper operation after completing the test.

Direct Measurement
Note: Direct measurement requires an analog DC micro-ammeter capable of reading to 0.01-microampere accuracy. No signal converter required.
1. Disconnect all power to the appliance.
2. Connect the test harness between the valve control and the pilot burner.
a. Insert the banana plug connected to the valve side of the test harness into the positive (+) jack on the DC microammeter as shown in Figure 2a.
b. Insert the other banana plug connected to the pilot burner side of the test harness into the negative (-) jack on the DC micro-ammeter as shown in
Figure 2a.
3. Reconnect power to the appliance.
4. Generate a call for heat.
5. Make sure the pilot flame lights and the main burner does not light.

6. After the pilot flame is on for ten seconds, read the DC micro-ammeter. The readings must be steady.
7. Take the action recommended in Table 1.

Millivolt Measurement
Note: Millivolt measurement requires a digital voltmeter capable of reading DC millivolts. Use the signal converter included with this kit. See Figure 2b.

1. Disconnect all power to the appliance.
2. Connect the signal converter to the voltmeter.
3. Set the voltmeter to read DC millivolts.

Note: The signal converter is not polarity sensitive.

4. Connect the test harness between the valve control and the pilot burner.
a. Insert the valve side of the test harness through the female end of the signal converter connector and into the positive (+) jack of the digital voltmeter, as shown in Figure 2b.

b. Insert the pilot burner side of the test harness through the female end of the signal converter connector and into the negative (-) jack of the digital voltmeter, as also shown in Figure 2b.
5. Reconnect power to the appliance.
6. Generate a call for heat.
7. Make sure the pilot flame lights and the main burner does not light.
8. After the pilot flame is on for 10 seconds, read the digital voltmeter. The readings must be steady.
9. Take the action recommended in Table 1.

The SmartValve™ Input Voltage Test Harness available for troubleshooting these systems is Honeywell Part # 396085. The Measuring SmartValve™ System Flame Current (Part # 395466) is the kit to measure Microamps.
There will be more on troubleshooting SmartValve™ in the next article.

Finally, I love to teach and would love to have you join us for some training. We conduct seminars on the following topics and many others:

One-Day Course:
• Powerpile Systems

Three-Day Course:
• Combustion Testing Design Gas Equipment
• Conversion Burners

Four-Day Course Designed for Your Specific Need:
• Modulating/Condensing Boilers

Five-Day Course:
• Fundamentals of Gas
• Circuitry and Troubleshooting
• Hydronic Controls
• Electric Ignition Systems
• Advanced Electric Ignition Systems

For more information, Tel: 401-437-0557; E-mail: timmcelwain@gastcri.com or write to: Gas Appliance Service Training & Consulting, 42 Village Dr., Riverside, RI 02915. ICM

Part IV, from the Jan/Feb 2022 Indoor Comfort

Parts I & II, from the Jul/Aug and Sep/Oct 2021 Indoor Comfort can be found here.

Part III, from the Nov/Dec 2021 Indoor Comfort can be found here.

I invite you to visit our new Facebook page I look forward to seeing you there.

SmartValve™ Generation I & II Troubleshooting
The troubleshooting of the SmartValve™ itself is fairly simple. We will, however, incorporate the valve into some actual systems. We will address a forced warm air system first. The low voltage portion of a warm air system is shown in Figure 1 with an EFT (Electronic Fan Timer). The line voltage portion of the system is shown in Figure 2.

Figure 3 illustrates a method of using a multimeter. That is grounding one lead of the meter to the common side of the transformer, the “C” terminal, and leaving it there. The other lead is used to go from control to control to check for voltage.

The best place to start troubleshooting is at the output to the igniter shown in Figure 4. With the thermostat calling or not with power applied, you should have 24 volts at that location. If there are 24 volts there you know the transformer is good, the 120 volts are good. If you have problems, then it is probably in the igniter sensor. One more important time-saver is—when troubleshooting with a combustion air blower on the equipment—if the blower runs, the 24 volts and 120 volts are okay. Obviously if there is a problem with 120 or 24, the combustion air blower would not run. If you have 24 volts at the output terminals and the system does not light, then the problem is with the igniter itself.

At the same time, with the igniter sensor disconnected, switch your meter over to the ohms scale and check the igniter resistance by going across the two terminals connected to the blue wires as illustrated in Figure 5. A new igniter is usually 2–4 ohms resistance. Up to 10 ohms is okay; anything over 10-ohm will require igniter replacement.

If you do not have 24 volts at the output to the igniter, then check power to the valve at the control plug as shown in Figure 6:

Electrical connections:
• 24 volt common goes to the grounded side of the transformer secondary—“C” on the transformer.

• 24 volt hot goes to the hot side of the transformer secondary—“R” on the transformer.
• Thermostat terminal brings the call for heat signal from the thermostat or pressure switch, depending on the type of equipment and control circuit.
• The thermostat does not carry the igniter current.
• Anticipator setting is .3 amps safely within the adjustment range of all electromechanical thermostats.

The Electronic Fan Timer (EFT) signal is on whenever the main valve is open and:
• Tells when to start timing the Fan-On delay.
• Tells when to start timing the Fan-Off delay.

In checking the control plug, as shown in Figure 7, you should have 24 volts at all times when the power is on. This is the uninterrupted voltage. If 24 volts are not measured here, check the transformer. If you have 24 volts here, check the two right-hand terminals as shown in Figure 8. If there are not 24 volts on the terminals, one of the controls is open in either the thermostat, limits or even the pressure switch.

It is also a good idea to make sure that there is no appreciable loss of voltage in the conditions of under load (thermostat calling) shown in Figure 9 and no load (no call for heat) shown in Figure 10. Whether load or no load, voltage should remain between 19 to 28 volts.

The SmartValve™ system needs an uninterrupted 24 volts to run the electronics in the valve and then a 24-volt signal through the thermostat circuit on a call for heat. By using the correct size transformer, a stable voltage should be able to be maintained. When the SmartValve™ has energized the igniter, check the voltage; if the voltage holds up under that load, it should remain a stable 24 volts. The more it deviates from the 24 volts, the more the problem is likely to be the transformer, or perhaps the line voltage to the transformer. It could also be an indication that the valve is increasing appreciably in resistance, thereby demanding greater current flow and causing the voltage to decrease.

Microamps
The ability to prove the flame and safely light the main burner is accomplished by the process of flame rectification. The Generation I electronic systems produce a 24-volt superimposed voltage from within the valve electronics. This signal is passed through the flame and produces a DC microamp signal of 0.3μ amp minimum. This voltage determines the intensity of the microamp signal. If the system is not working correctly, this check will be the first step in proving if the problem is microamps or the valve itself. For readings:

• The Generation I signal is 24 volts
• The Generation II signal is 80+ volts

See the Generation I and II signals in Figure 12. These voltages can be checked. With the igniter plugged into the gas valve (the illustration in Figure 11 shows it unplugged; it should be plugged in), ground one lead of the multimeter to ground (the gas valve is a good ground) while the other lead is inserted at the back side of the pilot harness on the black or clear wire microamp wire. Note: a paper clip fits nicely into the back of the harness for this reading.

If the readings are less than required, then replace the SmartValve™. Note: microamp readings cannot be obtained unless you have a special test harness, which is discussed later in this article. The minimum microamps for each generation is shown in Figure 12.

Flame proving circuit:
• About 0.3 microamps D.C. for the first generation SmartValve™. It uses 24 volts in the flame-sensing circuit and so the flame current is relatively small.

In addition to voltage checks, another indicator is the status of the igniter. This can be in the place of microamp readings

• If the igniter is off and the pilot is lit, but the main valve will not open, then the problem is not in the sensing circuit (Microamps) but in the main valve. If the igniter is off, you know the flame has been detected.
• If the pilot is lit and the igniter is still glowing, but the main valve will not open, then the problem is in the sensing circuit.

On Warm Air Systems, there will be an output signal available from the SmartValve™ to trigger the Electronic Fan Timer (EFT). It is the fourth terminal located on the lower left-hand side—a backwards “D” shape.

The signal is on whenever the main valve is open and is a DATA signal to the microprocessor on the circuit board. It:

• Tells when to start timing the Fan-On delay
• Tells when to start timing the Fan-Off delay

The output from this terminal on the connector can be measured and should be between 15 to 28 volts AC. This can be measured by placing a paper clip, attached to the alligator clip on the meter lead, and inserting it into the back of the control plug as shown in Figure 13 (the plug is shown detached; it should actually be plugged into the valve). It should be placed between Common and the EFT output terminal. You could also obtain this reading by using the Input Voltage Test Harness.

There is a SmartValve™ Input Voltage Test Harness available for troubleshooting these systems. It is Honeywell Part No. 396085. There is also a kit to measure Microamps. It is Measuring SmartValve™ System Flame Current, Part No. 395466.

We will discuss troubleshooting the Smart-Valve™ in an upcoming issue. ICM

Timmie M. McElwain is President of Gas Appliance Service, which provides training for those servicing gas combustion equipment. He is a certified instructor and test proctor for the Propane Gas Association in their CETP program.

Part III, from the Nov/Dec 2021 Indoor Comfort

Parts I & II, from the Jul/Aug and Sep/Oct 2021 Indoor Comfort can be found here.

We will start with the basics and then continue to operation, typical problems, diagnosis, troubleshooting procedures and a final solution to your particular problem. It’s easy to jump to conclusions with these systems and just change parts to hopefully solve a problem. That is, however, time-consuming and costly.

I invite you to visit our new Facebook page Timmie’s Tips on Gas. I look forward to seeing you there.

SmartValve™ Typical Wiring
The wiring for the SmartValve™ is fairly simple; it is not much more complicated than wiring for a standing pilot 24-volt system. Figure 1 shows an example of the typical wiring required. It needs a constant, uninterrupted 24 volts to run the electronics in the valve and a 24-volt signal that comes through the thermostat circuit and limits.

A 40 VA transformer, which is National Electrical Manufacturers Association (NEMA) rated Class II Standard DC20-92, is required for the SV9500 series and a 50 VA for the SV9600 Series. The igniter draws about 1.25 amps and the total current required is about 1.5 amps. Figure 2 shows the capacity and versatility of a NEMArated transformer.

NEMA standards for transformers specify how well the transformer must hold its output voltage under load conditions, as illustrated in Figure 2:

Voltage regulation:
• Nominal rating = 24 volts
• Open circuit = between 26 and 27 (no more than 27 volts)
• Full load = 23 to 25 Volts
• Twice full load = 20 to 23 Volts

SmartValve™ power requirements:
• Valve + igniter + thermostat + fan timer = 1.55 to 1.87 amps

37.2 to 44.9 VA
• Load on 50 VA transformer =
• 40 VA transformer load = 93 to 112%

A lower quality transformer is likely to have the voltage drop off much more rapidly so it will have a higher open circuit voltage. It will also have a lower voltage at 200% of rated load to get to 24 volts at full load.

Making connections
One of the changes made from Generation I to II was moving the system connector plug from the side to the top of the control, as illustrated in Figure 3. This plug can be unplugged for service and checkout when necessary; we will expand on troubleshooting in an upcoming column.

In Figure 4, we have an expanded view of the system connector. Looking at the connector with the clip to the right, the upper left square terminal is 24 volts hot (the “R” terminal from the transformer). To the right is the backwards “D” shaped plug, which is the common terminal (the “C” terminal from the transformer).

The lower right square terminal is the interrupted 24 volts through the thermostat (the anticipator setting is 0.3 amps) and limit controls. The lower left backwards “D” terminal is the EFT (Electronic Fan Timer) output terminal. This is a microprocessor “DATA” signal superimposed on an AC voltage feed to the electronic fan timer to determine the start of the fan on delay timing cycle. It also tells when to start timing the fan-off delay. We will discuss more of this troubleshooting, connector testing and the use of a test harness in a following column.

The other plug on top of the SmartValve™ is for the pilot burner, as shown in Figure 5. The pilot connections are 24 volts to the igniter on the two blue wires. The clear wire, or in some cases the black wire, is for the microamp flame signal to get back to the electronics in the valve, as illustrated in Figure 6. This pilot plug-in becomes an excellent point to start troubleshooting on this system; we will discuss more in an upcoming column.

Part numbers
Some miscellaneous information on SmartValve™ Generation I and II concerns natural/liquid propane (LP) conversion and part numbers for orifices and kits for accomplishing conversion. These are shown in Figure 7.

Figure 8 and Figure 9 break down the nomenclature for Generation I and II along with Generation III controls. It also includes the SmartValve™ water heater control numbers.

A list of Universal SmartValve service part replacement numbers that are still being produced, as well as obsolete numbers, can be found in the Tradeline Catalog Cross Reference.

Electronic Fan Timer Output Terminal
Back in Figure 4, we mentioned the “lower left backward D” shaped terminal. This is the Electronic Fan Timer (EFT) output terminal. This is a microprocessor “DATA” signal superimposed on an AC voltage feed to the electronic fan timer to determine the start of the fan on a delayed timing cycle. It also tells when to start timing the fan-off delay. To expand on this, “DATA” is a signal that rides “piggy back” on the AC signal. It carries electronic information to affect the operation of the timer. We will cover troubleshooting SmartValve systems in the next issue of ICM. ICM

Timmie M. McElwain is President of Gas Appliance Service, which provides training for those servicing gas combustion equipment.
He is a certified instructor and test proctor for the Propane Gas Association in their CETP program.

Part 1 (From Indoor Comfort, Jul/Aug 2021)

It does not matter if it is a forced warm air furnace or a forced hot water boiler—the same basic system is used to perform safe ignition followed by consistent operation throughout the entire call for heat.

There are, however, different ways the system is applied from intermittent pilot application to direct spark ignition and including hot surface ignition. Each has its own distinct advantages and problems. In this next series, we’ll attempt to resolve those burner problems related to these systems as well as offer corrections and diagnostics.

We will start with the basics and continue to operation, typical problems, diagnosis, troubleshooting procedures and hopefully a final solution to your particular problem. It’s easy to jump to conclusions with these systems and just change parts to hopefully solve the problem. That is, however, time consuming and costly.

I invite you to visit our new Facebook page Timmie’s Tips on Gas, it is located here. I look forward to seeing you there.

The Honeywell Smart Valve story
In this article, we are going to cover the Honeywell Smart Valve systems and discuss Generation I and Generation II. Generation I is obsolete, but controls from that series may still be in the field.

Smart Valve is the name Honeywell has given a unique ignition system developed in 1993. The Smart Valve combines all the best features of intermittent pilot ignition and hot surface ignition. It utilizes a pilot to light the main burner. It uses a glowing 24-Volt igniter to light the pilot light instead of a spark. There have been two Smart Valve systems. The first generation was manufactured from 1993–1997. Generation I included SV 9500, SV9501, 02 (0.5″ x 0.5″ pipe and 200,000 BTUs) and SV9600, SV9601, 02 (0.75″ x 0.75″ pipe and 415,000 BTUs). The new generation is still in production at the present time.

System controls & application
The SV9401/ SV9402/ SV9403, SV9501/ SV9502/SV9503 and SV9601/ SV9602 SmartValve System Controls combine gas flow control and electronic intermittent pilot sequencing functions into a single unit. This product family offers several different intermittent pilot sequences for a wide range of applications. See Table 2 for specific sequences available. The Q3450 or Q3480 intermittent pilot hardware provides low voltage ignition, flame sensor and pilot burner. This system is suitable for application in a wide range of gas-fired appliances including furnaces, rooftop furnaces, boilers, unit heaters, infrared heaters, space heaters, water heaters, decorative appliances and commercial cooking units. The specific application of the SmartValve System is the responsibility of the appliance manufacturer. See Table 3 for gas capacity and thread sizes.

The Tradeline SV9501 and SV9502 SmartValve models are replacement controls only for the SV9500, SV9501 and SV9502 models. Do not use these controls to replace other types of intermittent pilot or direct ignition controls. Do not use other controls to replace SmartValve models; the controls might fit, but the gas flow control functions might not be compatible with the appliance.

The Tradeline SV9602 SmartValve models are replacement controls only for the SV9500P, SV9501 P, SV9502P, SV9600P and SV9601 P models. The SV9602 is a prepurge, step-opening model.
1. Prepurge is normally 30 seconds.
2. The step-opening function provides a timed step outlet pressure at the start of each heating cycle to allow main burner ignition at reduced outlet pressure.
3. Reducer bushings are provided with the SV9602 and SV9601 models to adapt to smaller pipe sizes.
4. Ignition system controls with standard opening regulators (SV9501M, SV9502M and SV9601M) or slow opening regulators (SV9501 and SV9502H) can be converted between natural gas and liquefied petroleum (LP) gas.
5. Ignition system controls with step-opening regulators (P suffix) cannot be converted between gases.

Pilot burners
The first difference you see is the pilot burner—a standard Honeywell burner similar to the Q314. What is unique is the ignition source for the pilot:
• Small igniter in front of the pilot
• Powered by 24 Volts
• Glows red hot on a call for heat to light the pilot.

The igniter is made of silicon nitride, which is similar to the material used for hot surface igniters. It is, however, stronger and is well-protected by the pilot burner and ground strap so that it does not break unless it receives unusual abuse. The igniter has a positive coefficient with a relatively low resistance when cool. Therefore, the initial current flow makes it heat up very fast. The pilot usually lights in a few seconds. The flame rod is positioned to “prove” the pilot. Flame rectification is used to prove the pilot flame is burning. When the flame is detected the igniter is turned off. The main valve opens. Flame rectification provides fast, sensitive flame detection.

The igniter flame rod assembly is replaceable without having to replace the entire pilot, which is a great advantage over intermittent pilot systems. The original pilot and harness that plugs into the valve (Part No. Q3400A-1024) was an unshielded version. A shielded version (Part No. Q3400A-1115) was released due to problems with pinching the cables and getting a feed over of 24 Volts on the microamp wire. The blue wires on the harness are for 24 Volts to get the igniter to glow. The first versions had a clear wire, which was for the microamp signal back to the electronics on the valve. It was later changed to a black wire. The Generation I valves used 24 Volts as a superimposed signal and they had a minimum microamp signal of .3 microamps. Generation II uses 80 + Volts to create a minimum signal of 1.3 microamps.

The pilots are the Q3450 (Figure 1 and Figure 2), which is a lower input pilot, and the Q3480 (Figure 3) version, which has a little higher input.

The Smart Valve is a dual valve (redundant) valve based on the VR8200 and VR8300 series of gas valves. The dual valve feature guards against the possibility of a passing gas valve. The capacity goes all the way up to 415 cubic feet per hour and has a 1″ W.C. pressure drop at 300 CFH.

Figure 5 shows that the first valve is a solenoid valve, which opens upward and is actually the PV (pilot valve). It is designed in such a way that if pressure in excess of 14″ W.C. is applied to the valve, it may not open. This is a safety feature to prevent over-pressure and possible damage to the diaphragm valve. The second valve is the servo valve (a diaphragm valve controlled by the servo regulator); it is typically the MV (main valve). The second servo valve will not be powered until the flame is proven by rectification.

There are various models available to manufacturers:
• Standard open (M model)
• Slow open (H model)
• Step open (P model)

The M and P models are rated for -40°F so they can be used on rooftop units or other unheated spaces. Replacements for many models can be found in the Honeywell Tradeline catalog or at customer.honeywell.com.

The valves can be used with natural or LP gases. The exception is the P model (step opening), which can’t be converted. There are conversion kits available:
• Natural to LP 393691
• LP to Natural 394588

There are also pilot orifices available for the Q3450 pilot:
• Natural BCR18 (.018)
• LP BBR 11 (.011)

Figure 6 illustrates the different opening characteristics of SmartValve Standard open valve:
• Fast open
• Reaches full rate in 1–2 seconds, depending on capacity
• On some applications, particularly low firing rates, there is little variation in regulation for a half second when it first turns on

Slow open valve
• Takes about 4–5 seconds to get fully open
• Under maximum capacity, it may even take 9–10 seconds to get fully open
• Again, for service, replace with slow open

Step open
• Valve opens to some fixed (non-adjustable) low rate for light-off, and after 10 seconds, goes to full rate
• For service work, replace with step opening only as there may be ignition problems with any other opening characteristic
• Equipment manufacturers chose step open (at higher cost) for a reason
• Usually used to make light-off smoother or to cure light-off problems

When the Smart Valve receives a call for heat, there is an immediate surge of current due to the low resistance through the igniter (low cold resistance). Silicon nitride has a positive temperature coefficient. Line voltage igniters have a negative temperature coefficient. The hot resistance is high. There is a 22.5 Volt drop across the igniter and a 1.5 Volt drop across the pilot valve relay coil. The pilot valve relay coil is immediately energized, pulling in the pilot valve. On the original Generation I Smart Valve there was continuous trail for ignition—the igniter came on and stayed on until the system lit off. Generation II has continuous retry with a 90-second trial for ignition followed by a 5-minute wait period if ignition does not take place.

During the 90-second attempt at ignition, the igniter will be on for 30 seconds, then shut off for 25 seconds, then back on for 30 seconds. This is to keep from overheating the pilot relay and to extend the life of the igniter.

SV9501 (Generation II) features
The new features of Generation II of the Smart Valve include:
• Meeting new Z21.20 requirements
• Switch provides manual shutoff
• Soft element warm up
For direct replacement for the SV9500, or Generation I, you should be aware of the following:

• Same package shape and size
• Same Q3450 pilot burner
• Identical connectors (power connector on top)

The steps for the Call for Heat are as follows:
• Start check (three seconds)
• Trial for ignition (90 seconds)
• Pilot valve open
• HSI on (30 seconds)
• HSI off (25 seconds)
• HSI on (30 seconds)
• Pilot valve closed /HSI off
• Retry delay (five minutes)
• Trial for ignition
• Retry delay
• Cycle continues until pilot lights/proves or the call for heat ends.

For theQ3450 & Q3480 pilots, the pilot igniter and flame rod assembly on both the Q3450 and the Q3480 need to be field replaced. Figure 7 gives an illustration for doing so. The directions are as follows:

Replace Igniter-Flame Rod Assembly
1. Turn off the furnace at the circuit breaker or fuse box.
2. Remove the spring clip, then the igniter-flame rod assembly from the pilot burner.
3. Disconnect the igniter-flame rod assembly keyed plug from the igniter connection on the SV9500/SV9600.
4. Remove the igniter-flame rod assembly from the furnace.
5. Install replacement igniter-flame rod assembly in the pilot burner and secure it with the spring clip.
6. Connect igniter-flame rod assembly keyed plug to igniter connection on the SV9500/SV9600.
7. Turn on power and set the thermostat to call for heat. The pilot should light and then the main burner should lights.
Note: Sensor tip must be in pilot flame.

Adjust Pilot Flame
The pilot flame should envelop approximately 3/8″ (10mm) of the sensor tip.

To adjust pilot flame:
1. Turn off system by setting thermostat below the temperature to call for heat.
2. Disconnect lead to MV terminal on SV9500/SV9600.
3. Light pilot by setting the thermostat to call for heat.
4. Remove pilot adjustment cover screw from gas control.
5. Turn inner pilot adjustment screw clockwise to decrease or counterclockwise to increase pilot flame.
6. Always replace pilot adjustment cover screw and tighten firmly after completing adjustment to assure proper operation.

The Generation I system used a 24 Volt signal for rectification and had a minimum microamp signal of 0.3 microamps, which proved to be somewhat of a problem as it was too low and caused some nuisance shut-downs. Generation II went to a minimum voltage signal of 80+ Volts with a minimum microamp signal of 1.3 microamps. The flame-proving circuit is illustrated in Figure 8. A complete discussion on flame rectification is in our manual Electric Ignition Systems Volume I.

Figures 9, 10, 11 and 12 illustrate the physical differences between Generation I and II. The SV9500 with the on/off knob easily distinguishes it from the Generation II SV9501 and SV9502. In addition to the Generation II having a switch, the control harness connector was moved from the side to the top. Also shown is the use of the flange kit, which makes for ease when replacing a valve, as the 9/64″ hex screws and the valve can be easily removed by using a wrench to unmake the threaded portion of the valves.

Figure 11 and Figure 12 also shows other typical characteristics of the valves, such as the pressure regulator adjustment, pilot outlet, inlet and outlet pressure taps for testing gas pressures with a manometer. The electrical connections visible on Generation II on top of the valve are the igniter connector and the control circuit connector.

Part 2 (From Indoor Comfort, Sep/Oct 2021)

Honeywell SmartValve
In this article, we continue our discussion of the Honeywell SmartValve. SmartValve is the name Honeywell gave a unique ignition system developed in 1993. The SmartValve combines all the best features of intermittent pilot ignition and hot surface ignition. It utilizes a pilot to light the main burner and a glowing 24-Volt igniter to light the pilot instead of a spark.

There have been two SmartValve systems. The first generation was manufactured from 1993–1997. The new generation is currently still in production. Generation I includes SV9500 and SV9501, 02 (1/2″ x 1/2″ pipe; 200,000 BTUs), as well as SV9600, SV9601, 02 (3/4″ x 3/4″ pipe; 415,000 BTUs).

Picking up where we left off in “The Gas Side—Honeywell Gas Valves: Part 1” in ICM’s July/August 2021 issue, here are directions for Standard Pressure Regulator (M Models), Slow Open (H Models, Step Open [P Models]):

1. Check the full rate manifold pressure listed on the appliance nameplate. The ignition system control outlet pressure must match the full rate pressure listed on the nameplate. Adjust the pressure if they do not match. Note: Slow opening (H models) and step opening (P models) may take several seconds to reach full flow rate. M models will take 2–3 seconds to reach full flow rate.

2. With the main burner On, check the ignition system control flow rate using the meter clocking method, or check the pressure using a manometer connected to the outlet pressure tap on the ignition system control.

3. Adjust the pressure regulator to match the appliance rating if necessary. See Table 2 and Table 3 for factory set nominal outlet pressure and adjustment range.

a. Remove the pressure regulator adjustment cap screw.
b. Using a screwdriver, turn the inner adjustment screw clockwise to increase or counter- clockwise to decrease gas pressure to the burner.
c. Replace the cap screw and tighten it firmly to prevent gas leakage.

4. If the desired outlet pressure or flow rate cannot be achieved by adjusting the ignition system control, check the ignition system control inlet pressure using a manometer at the ignition system control inlet pressure tap.

5. If the inlet pressure is in the factory-specified nominal range, as shown in Table 2 and Table 3, the ignition system control.

Otherwise, take the necessary steps to provide proper gas pressure to the control. Note: If the burner firing rate is above the maximum capacity as shown in Table 3, it might not be possible to deliver the desired outlet pressure. This is an application issue, not a control failure. Take whatever steps are necessary to correct the situation.

Convertible (Natural/LP) Regulator for Mobile Home Applications
Ignition system controls with the suffix letter R are convertible pressure regulator models. They can be converted from natural gas to liquid propane (LP), or from LP to natural gas, without a conversion kit.

Before converting the ignition control from one gas to another, check the ignition control label and the appliance manufacturer rating plate to determine if the factory-set pressure regulator setting meets the appliance manifold requirements after conversion.

Note: Convertible pressure regulator models (suffix letter R) do not have field-adjustable regulators.

If the factory pressure regulator setting meets the appliance manifold requirement, convert the ignition control using the following procedure:
1. Remove the pressure regulator cap (see Figure 1).
2. Turn over the cap so the letters facing up are for the gas type the appliance uses—NAT for natural gas and LP for liquid propane gas.
3. Replace the cap and tighten firmly.

The original SmartValve had continuous trial for pilot ignition; the igniter and pilot gas would remain on indefinitely as illustrated in Figure 2.

SmartValve Generation II is a continuous retry version. It attempts to ignite with the igniter on and pilot gas flowing for 90 seconds. If there is not any ignition, then the igniter and pilot gas will shut down for five minutes. This is shown in Figure 3. The system will continue this sequence until ignition takes place or the power is shut off. There is not enough gas escaping during the try for ignition to reach the lower explosive limit of either natural or LP gases.

There is safety designed into the circuits, as the igniter is part of the valve control circuit. If the igniter is broken or otherwise electrically open, the valves cannot be opened; it is fail- safe.

Figure 4 is the sequence of operation for the older Generation I system. Depending on the version, there may be a different sequence of operation with Generation II as shown in Figure 5.

The SV9501 is the regular 90-second trial with the five-minute shutdown. The SV9502 will have the same trial times but will add prepurge at the beginning.
The SV9503 version is a single try with immediate hard lockout if ignition does not take place on the first try. This will require shutting the power off and reattempting another try for ignition. This system is used on many decorative fireplaces that use a switch on the wall to start the fireplace.
The sequence of operation illustrated in Figure 6 on a call for heat is that the pilot valve and igniter come on together when the thermostat calls for heat. The main burner opens only when the pilot is proved and remains open throughout the call for heat. The pilot burner also stays on during the entire call for heat. When the thermostat is satisfied, the pilot and main burner gas is shut off.

Figure 7 is the sequence of operation for the Generation II SmartValves.

In the next series, we will explore SmartValve’s typical wiring. ICM

Part 1 (From Indoor Comfort, Mar/Apr 2021)

As we look into some more modern systems and what specific problems they present, it is important to understand the basic fundamentals associated with these systems.
Most of our modern heating equipment in some way or another involves electronics, and with the electronics, the use of Flame Rectification as a safety and flame-proving system.
It does not matter if it is a forced warm air furnace or a forced hot water boiler—the same basic system is used to perform safe ignition and then consistent operation throughout the entire call for heat.
There are however different ways it is applied from Intermittent Pilot Application to Direct Spark Ignition and including Hot Surface Ignition. Each has its own distinct advantages and problems.
I invite you to visit our new Facebook page, Timmie’s Tips on Gas, located at facebook.com/groups/timmiesgastips. I look forward to seeing you there.
Universal Gas Valves Systems
In this section we are going to discuss Universal Gas Valves systems—in particular the Robertshaw 720-079 Gas Valve Uni-Kit. We will present some of the basics initially, then the installation and finally get into troubleshooting.
The 720-079 is designed to work equally well on Intermittent Pilot, Direct Spark and Hot Surface Ignition. Its features include:
• Dual automatic valves (redundant)
• Wiring connections, manual selector and adjustments on top of the valve
• Meets all codes requiring dual valve safety shutoff
• Reduces service truck stock-freeing up valuable space and saving money.

The 720-079 shown in Figure 1 features a manual selector, wiring connections and adjustments that are all easily accessible on the top of the valve. The 720-079 Uni-Kit has 1/2″ side outlets and a pressure regulator that is preset at 3.5″ water column (WC) for natural gas. For liquefied petroleum (LP) gas applications, the valve can be converted by using a pressure regulator conversion kit that is included.
The 720-079 incorporates a manual valve, pilot valve (dual automatic valves) and a main gas pressure regulator all in a small compact valve with a swing radius of 3–9/16″. The small size of the 720-079 lends itself to replacing many original equipment manufacturer (OEM) and competitive valves. The 720-079 is multiposition and can be mounted in any position, except upside-down.

The red manual selector arm easily identifies the 720-079 shown in Figure 2. In fact, all Robertshaw 7200 series valves with this arm are dual seated valves. The valve also features side outlets, which can be plugged if not used. Also illustrated are the inlet and outlet pressure taps and the regulator adjustment cap.

Figure 3 illustrates the capacities for different inlet and outlet sizes for the 7200 series. The 720-079 as shown in the ordering data is ½” x ¾” valve with a capacity of 150,000 BTUs. The cross-references in Table 1 cover White-Rodgers and Honeywell Valves.

Intermittent Pilot: Pilot Tubing
Figure 4 illustrates the installation instructions and wiring for intermittent pilot applications. The instructions for pilot tubing are as follows:
1. Make sure tubing is free of burns and dirt.
2. The pilot orifice must be checked and cleaned if necessary at this time.
3. Connect pilot tubing into the control using fitting provided and tighten for a gas tight seal.
Wiring
DO NOT short gas valve terminals. This will damage the wall thermostat and void the warranty.
1. Check the system for the proper transformer by comparing the volt amps (VA) ratings of the transformer and the system. The system rating is determined by multiplying the voltage draw x the amp draw. Normally 20VA transformers are sufficient for heating only applications and 40VA for heating/cooling applications. (Note: improper transformer VA rating will cause erratic system operation).
2. Connect the wire from the “MV” terminal on the ignition control unit to the “M” terminal on the gas valve.
3. Connect the wire from the “PV” terminal on the ignition control unit to the “P” terminal on the gas valve.
4. Connect the wire from the “MV/PV” terminal on the ignition control unit to the “C” terminal on the gas valve.
Hot Surface Applications: Pilot Tubing
Figure 5 shows the wiring and instructions for hot surface ignition (HSI) applications. The pilot plug must be in place as there is no need for a pilot. It can be either local sense using the igniter as a sensor or remote sense with a separate flame sensor. The instructions for pilot tubing are as follows:
Note: Some hot surface applications use the pilot outlet. If so, proceed as directed below. If not used, install pilot outlet tubing plug packaged in the 720-079 gas valve kit, then proceed to “wiring.”
1. Make sure tubing is free of burns and dirt.
2. We strongly recommend that the pilot orifice be checked and cleaned if necessary at this time.
3. Connect pilot tubing into the control using fitting provided, and tighten for a gas-tight seal.
Wiring
DO NOT short gas valve terminals. This will damage the wall thermostat and void the warranty.
1. Check the system for the proper transformer by comparing the VA ratings of the transformer and the system. The system rating is determined by multiplying the voltage draw x the amp draw. Normally 20VA transformers are sufficient for heating only applications and 40VA for heating /cooling applications. (Note: improper transformer VA ratings will cause erratic system operation).
2. Locate the white wire terminal adaptor (jumper) that is included with the 720-079 gas valve.
3. Connect the white wire terminal adaptor to the “M” and “P” terminals on the 720-079 gas valve.
4. Determine which wire was connected to the “main valve” terminal on the original valve. Connect this wire to the remaining terminal on the white wire terminal adaptor.

Direct Spark: Pilot Outlet
Figure 6 illustrates the wiring and instructions for direct spark ignition either remote or direct sense. The installation instructions for the pilot outlet are:
First, install the pilot tubing plug packaged in the 720-079 gas valve.
Wiring
DO NOT short gas valve terminals. This will damage the wall thermostat and void the warranty.
1. Check the system for the proper transformer by comparing the VA ratings of the transformer and the system. The system rating is determined by multiplying the voltage draw x the amp draw. Normally, 20VA transformers are sufficient for heating-only applications and 40VA for heating/cooling applications. (Note: improper transformer VA rating will cause erratic system operation).
2. Locate the white wire terminal adaptor (jumper) that is included with the 720-079 gas valve.
3. Connect the white wire terminal adaptor to the “M” and “P” terminals on the 720-079 gas valve.
4. Determine which wire was connected to the “main valve” terminal on the original valve. Connect this wire to the remaining terminal on the white wire terminal adaptor.
5. Connect the remaining wire from the original gas valve to the “C” terminal on the 720-079 gas valve.

Operating Instructions
The operating instructions are as follows:
1. Turn the wall thermostat to its lowest setting. Remove burner access panel(s). Selector arm must only be operated by hand (see illustration in Figure 7). Do not use pliers, wrenches or other tools to operate the arm. The selector arm cannot be moved into the Off position without first depressing the lever in the On position.
2. Move selector arm to the Off position.
3. WARNING: Wait at least five minutes to allow any gas in the combustion chamber to vent; if you then smell gas in the appliance area or near the floor, STOP and follow warning instructions. Failure to do so may result in fire or explosion.
4. Move selector arm to the On position, and set room thermostat to desired temperature. Allow burner to cycle on and off.
5. Leak test with a soap solution after installing with main burner on. Coat pipe and tubing joints, gasket, etc. with soap solution. Bubbles indicate leaks.
6. Replace burner access panel.
Pressure Regulator Adjustments
An adjustment of the pressure regulator is not normally necessary since it is preset at the factory. It may need to be adjusted, however, to maximize the combustion efficiency of the equipment. (Note: manometer attachment may be accomplished at pressure tap plug, above control outlet, as shown in Figure 7. It is also a good idea to measure inlet pressure at the tap on the other side of the valve). Field adjustment may be accomplished as follows:
1. Manometer or gauge attachments may be accomplished at pressure tap plug (D).
2. Remove regulator adjustment screw cap (top of control-A).
3. With small screwdriver, rotate adjustment screw (B) clockwise to increase, or counterclockwise to decrease, pressure to comply with manufacturer’s specifications.
4. Replace regulator adjustment screw cap (A).

Regulator Conversion
Caution: main burner and pilot orifices must be changed when regulator is converted from one type of gas to another.
1. Turn off gas and electricity to appliance.
2. Remove slotted cap (A), adjusting screw (B) and natural gas spring—not color-coded— (C), from control.
3. Install new LP spring—color-coded with a black strip.
4. Install new adjusting screw (B).
5. Attach manometer or pressure gauge at the outlet pressure tap (D).
6. Turn gas and electricity on.
7. Turn room thermostat to call for heat.
8. With burner on, adjust screw (B) to supply LP gas to pressure as recommended by the appliance manufacturer.
9. If adjusting screw (B) reaches its maximum depth (bottoms out) before recommended pressure setting is reached, turn screw counterclockwise until pressure drops slightly (approximately 0.1″ WC)
WARNING: do not stretch or alter spring.
10. Turn off gas and electricity to appliance.
11. Remove manometer or pressure gauge and reinstall pressure tap outlet plug (D).
12. Install new red slotted cap in place of (A).
13. Turn gas and electricity On.
14. With burner operating, immediately check all fittings for leaks with soap solution. Bubbles indicate leaks that must be corrected.
15. Conduct a combustion test on the equipment to determine safe and efficient firing of the equipment.
16. Attach label to show control has been converted to LP.
17. Set room thermostat to desired temperature.

Part 2 (From Indoor Comfort, May/Jun 2021)

In this article, we will discuss Universal Gas Valves systems, in particular the White Rodgers 36E98-304 Universal Slow Opening Gas Valve. We will present some of the basics initially, then the installation and finally get into troubleshooting.
The 36E98-304-combination gas valve illustrated in Figure 1 is designed for intermittent ignition, direct spark ignition and hot surface ignition system applications. The valve is equipped with a redundant solenoid valve that controls gas flow to the pilot and main burners, a main valve that controls gas flow to the main burner, a pressure regulator to maintain a constant outlet pressure and a two-position gas cock knob for manual gas shut off. It uses a 0.008 internal orifice to cause the slow opening affect. Do not use this valve to replace White-Rodgers 36E02, 36E37 or 36E97 slow opening valves; they use different orifices and have different opening characteristics.

The pipe size/capacities are from 3/8″x 3/8″ giving 75,000 British Thermal Units (BTUs) for natural gas and 121,500 for liquefied petroleum (LP) gas to 0.5″x 0.75″ giving 125,000 for natural gas and 202,800 for LP gas.

The valves are shipped with the pilot outlet plugged. For installations requiring a pilot, remove the plug and use the fitting supplied separately with the control. Figure 2 shows location of pilot outlet along with outlet pressure tap. Features include:
1. Poppet style manual valve (capable of withstanding high inlet pressures)
2. Conical inlet and outlet screens protected from pipe damage
3. High sealing force direct acting solenoid valves
4. Controlled gasket clinch between castings to with stand high inlet pressures
5. Tamper-resistant screws
6. Automated assembly and test
Figure 3 shows the correct piping procedures. Figure 4 illustrates the internal operation of the gas valve.

Valve features and performance
The next few sections illustrate some of the features and options on this valve series. Not all of these features may be found on equipment you run into but they are options that Original Equipment Manufacturers (OEMs) can choose for their particular equipment.
Table 1 illustrates the particulars of the one-inch pressure drop capacity.

Features & Options: Fast Open Control
This control has a fast-opening characteristic that is suitable for a wide range of applications. It provides a fast rise to full pressure upon energizing the main and redundant solenoid. Regulator spring conversion kits are available for this control.
Features & Options:
Slow Open Control
This control has slow opening characteristic. It provides a slow increase of gas to full pressure for smoother ignition, as may be required by some applications. There is also a 36E36-304 fast opening valve from White-Rodgers that is classified a universal replacement valve. There is a cross-reference for this valve in Table 2. It has all the other wiring and other characteristics of the 36E98-304 other than its opening time.
Intermittent Pilot Directions

See Figure 5.
1. Connect wire from “MV” terminal on ignition control unit to “M” terminal on gas valve.
2. Connect wire from “PV” terminal on ignition control unit to “P” terminal on gas valve.
3. Connect wire from “MV/PV” terminal on ignition control unit to “C” terminal on gas valve.

Hot Surface Ignition Directions
See Figure 6.
1. Connect tan wire terminal adaptor (jumper) included with gas valve to “M” and “P” terminals on gas valve.
2. Determine which wire was connected to “Main Valve” terminal on original valve. Connect this wire to remaining terminal of the tan terminal adaptor.
Features & Options: Delay Open Control
This control has delayed opening characteristic. This control is equipped with a pressure switch system.
Features & Options: Step Open Control
This control has a step open feature that regluates the outlet to an initial step pressure (non-field adjustable) and rises to the full outlet pressure. It provides a step pressure for softer ignition.
Features & Options: Two-Stage Control
This control has a two-stage feature. Upon energizing the main and redundant control valves, the servo regulator will provide a low fire rate until the high fire solenoid is energized. (Field adjustable on both low fire and high fire).
Features & Options: Convertible Control
The convertible regulator option for this control involves a construction that permits easy Natural to LP conversion (or vice versa) by removing, inverting and replacing the regluator cap screw. This feature easily lends inself to use in mobile homes and infra-red applications.
Table 2 gives the cross-reference for the 36E98-304-gas valve and includes the OEMs that use the old part listed.
Adjustment
Hot Surface or Direct Burner Ignition Systems Install jumper wire across M-1 and P-3 terminals. This will open both redundant valves together.
Manual Valve Knob
The manual valve knob is a two-position (on-off) type. To turn manual valve On, rotate knob clockwise or counterclockwise to line up the word On on the knob with the indicator on the cover casting as shown in Figure 7. To turn manual valve Off, rotate knob clockwise or counter-clockwise to line up the word Off on the knob with the indicator on the cover casting.

Pilot Gas Adjustment
These controls are factory preset to provide proper pilot gas flow for most applications. If additional adjustment is necessary, follow these steps:
1. Turn off all electrical power to the system before making any adjustments.
2. Remove the pilot adjust cover screw and gasket to expose the adjusting screw shown in Figure 8. Turn the adjusting screw clockwise to reduce pilot flame, or counterclockwise to increase pilot flame.
3. Replace the gasket and pilot adjust cover screw and tighten securely.
4. Restore power to the system.

Pressure Regulator Adjustment
These controls are shipped from the factory with the regulator set for 3.5″ W.C. (natural gas, full flow). Consult the appliance rating plate to ensure burner manifold pressure; it should be 3.5″ W.C. If another outlet pressure is required, follow these steps. If a valve has been factory-adjusted for the 2.5″–5″ W.C. range, it cannot be field-adjusted outside that range. This is also true for valves adjusted to the 7.5″–12″ W.C. range for LP gas.
1. Turn off all electrical power to the system.
2. Attach a manometer to the outlet pressure tap of the valve.
3. Turn on system power and energize valve.
4. Remove regulator cover screw and turn regulator adjust screw clockwise to increase pressure, or counterclockwise to decrease pressure, as shown in Figure 8. Always adjust regulator to provide the correct pressure according to the OEM’s specifications listed on the appliance rating plate.
5. Replace regulator cover screw and tighten securely.
Figure 9 is a top view of the valve showing the manual knob, pilot solenoid, electrical panel, main solenoid and the adjustment for the regulator. On all gas valves, only main gas is regulated. The pilot is on line pressure and is adjusted by the screw, to the right of the manual knob.

Please contact assteditor@indoorcomfortmarketing.com for graphs concerning the 1″ pressure drop capacity and performance curves for the gas valves in this series, as well as an overview of gas valve models available. ICM
————————————————————-
Timmie M. McElwain is President of Gas Appliance Service, which provides training for those servicing gas combustion equipment. He is a certified instructor and test proctor for the Propane Gas Association in their CETP program.

Part One appeared in the September/October 2020 Indoor Comfort.
Operation
The VR8345 gas controls, Figure 9, provide an “On-Off” manual control of gas flow. In he Off position, pilot and/or main burner gas flow is prevented. In the On position, pilot and/or main burner gas flow is under control of the thermostat, the Direct Spark Ignition System (DSI) module, Hot Surface Ignition System (HSI) module/intermittent pilot module and the gas valve.

Direct Spark Ignition/Hot Surface Ignition Applications
System operation
When the thermostat calls for heat, the DSI or HSI module is energized, Figures 10 & 11. The module activates the first and second automatic valves of the gas control, which allows main burner gas flow. At the same time, the DSI/HSI module generates a spark at the igniter-sensor to light the main burner. The second automatic valve diaphragm, controlled by the servo pressure regulator, opens and adjusts gas flow as long as the system is powered. The servo pressure regulator monitors outlet pressure to provide an even main burner gas flow. Loss of power (thermostat satisfied) de-energizes the DSI/HSI module and closes the automatic valves. The system is ready to return to normal service when power is restored through the thermostat.
If the igniter-sensor stops detecting a flame at the main burner (lack of adequate microamp signal back to the module), then the trial for ignition is restarted. On DSI/HSI modules with lock-out timers, the automatic valves are de-energized and ignition stops after the lock-out period. On modules without lock-out timers, the trial for ignition continues indefinitely and the first automatic valves remain open.
If the main burner flame is restarted successfully, operation continues as described above. Gas control operation is described in more detail below.

Valve position during thermostat “Off” cycle
The valve is positioned as shown in Figure 12 when the:
• Gas control knob is in the On position.
• Thermostat is not calling for heat.
The first automatic valve is closed. The second automatic valve operator is de-energized, closing the channel to the pressure regulator, and opening a channel to the underside of the second automatic valve diaphragm. The combination of spring pressure under the second automatic valve diaphragm and lack of outlet pressure hold the diaphragm firmly closed. Both valves block the main burner gas flow.

When the thermostat calls for heat
When the thermostat calls for heat, the DI module generates a spark at the main burner and the first automatic valve and second automatic valve operators are energized (Figure 13). The first automatic valve opens, and the second automatic valve operator valve disk is lifted off its seat. This diverts gas flow from the second automatic valve diaphragm and causes a reduction of pressure on the underside of this diaphragm. The reduced pressure on the bottom of the automatic valve diaphragm repositions the diaphragm downward, away from the valve seat, allowing main burner gas flow.

Intermittent Pilot Applications
System operation
When the thermostat calls for heat, the S8600 Intermittent Pilot Module is energized. The S8600, in turn, activates the first automatic valve of the gas control, allowing pilot gas flow. Simultaneously, the S8600 module generates a spark at the igniter-sensor and lights the pilot. The pilot flame is then sensed by the igniter-sensor, and spark generation ends.
After the pilot is lit, the S8600 module energizes the solenoid for the second automatic valve operator (the first automatic valve remains energized). This is dependent upon an adequate microamp signal being produced as the flame is sensed by the igniter-sensor. That signal should be in the range of 2–10 microamps (3–5 being the normal range).
The second automatic valve diaphragm, controlled by a servo pressure regulator, opens and adjusts main gas flow as long as the system is powered and the pilot is burning. The servo pressure regulator monitors outlet pressure to provide an even main burner gas flow.
Loss of power (thermostat satisfied) de-energizes the S8600 module and closes both automatic valves. The system is then ready for the next cycle.
Loss of pilot flame, or when the flame is too small to reliably light the main burner, closes the second automatic valve operator. The S8600 module then attempts to restart the pilot. On S8600 modules with lock-out timers, the first automatic valve closes after the lockout period. On S8600 modules without lock-out timers, the trial for ignition continues indefinitely and the first automatic valve remains open.
If the pilot flame is restarted successfully, the main burner is reopened, and gas flows to the main burner as described above. Gas control operation is described in more detail below.
Valve position during thermostat “Off” cycle
The valve is positioned as shown in Figure 14 when the:
• Manual gas control now is in the On position.
• Thermostat is not calling for heat.
The first automatic valve is closed. The second automatic valve operator is de-energized, closing the channel to the pressure regulator, and opening a channel to the under-side of the second automatic valve diaphragm. The combination of the spring pressure under the second automatic valve diaphragm and lack of outlet pressure hold the diaphragm firmly closed (gas pilot burner gas flow is prevented by the first automatic valve and the main burner by both valves).

When Thermostat Calls for Heat
When the thermostat calls for heat, the trial for pilot ignition begins. The first automatic valve solenoid is energized by the module and opens, allowing pilot burner gas flow. Gas also flows to the second automatic valve operator, but is mechanically blocked at the operator (see Figure 12).
After the pilot lights and the pilot flame is sensed by the igniter-sensor, the second automatic valve solenoid is energized by the module, and the second automatic operator valve is lifted off its seat (see Figure 13). This diverts gas flow from the second automatic valve diaphragm and causes a reduction of pressure on the underside of this diaphragm. The reduced pressure on the bottom of the automatic valve diaphragm repositions the diaphragm downward, away from the valve seat, allowing main burner gas flow.
All Applications
During the On cycle, the servo pressure regulator provides close control of outlet pressure; even if inlet pressure and flow rate vary widely. Any outlet pressure change is immediately reflected back to the pressure regulator diaphragm, which repositions to change the flow rate through the regulator and, thus, through the automatic valve.
If outlet pressure begins to rise, the pressure regulator diaphragm moves slightly higher, allowing less gas flow to the gas control outlet. This increases gas pressure under the automatic valve diaphragm and repositions the valve disk closer to the seat. Thus, flow of gas through the second automatic valve is reduced and outlet pressure falls to the desired level.
If outlet pressure begins to fall, the pressure regulator diaphragm moves slightly lower, allowing more gas flow to the gas control outlet. This decreases gas pressure under the second automatic valve diaphragm and repositions the valve disk further from the seat. Thus, flow of gas through the second automatic valve is increased, and outlet pressure rises to the desired level.
When the call for heat ends
When the call for heat ends, the first automatic valve and the second automatic valve operator close, bypassing the regulator(s) and shutting off the main burner (and in the intermittent pilot application, the pilot gas flow). As pressure inside the gas control and underneath the automatic valve diaphragm equalizes, spring pressure closes the second automatic valve to provide a second barrier to gas flow. ICM