The importance of universal controls cannot be emphasized enough. The ability to carry one control that covers a multitude of applications makes the service technician’s job a lot easier. There are other control systems that also have universal controls that can be used. We are seeing electronic fan timers with a universal board that replaces many controls. We will be discussing some of those in later articles. There are also universal integrated furnace controls. Keeping truck stock simple and convenient is what it is all about.
Honeywell’s VR8345M Universal Electronic Ignition Gas Control (Figure 1) is used in gasfired equipment with capacities up to 300 cubic feet per hour at a one-inch water column pressure drop for natural gas. The VR8345M will operate with direct spark ignition (DSI), hot surface ignition (HSI) or intermittent pilot ignition.
The control includes a manual valve, two automatic operators, a pressure regulator, pilot adjustment, pilot plug and ignition adapter. It is also:
• Compatible with hot surface pilot, intermittent pilot and direct spark ignition.
• Replaces virtually any IP, HSI or DSI gas control.
• For use with 24 VAC heating appliances that burn natural or manufactured gas or liquefied petroleum (LP) gas (it includes a converter kit to adapt from natural gas to LP gas).
• Compact to fit into tightly packed, high efficiency heating equipment.
• Works with virtually all residential equipment and all but the largest commercial equipment, with a regulation capacity range of 30,000 to 415,000 BTU per hour natural gas (48,600 to 672,300 LP gas).
• All adjustments and wiring connections are accessible from the top of the control.
• Has a straight-through body pattern.
• Includes 1/8-inch NPT inlet and outlet taps on top of the gas control to aid the adjustment of gas pressure in problem installations.
• The 3/4-inch x 3/4-inch inlet and outlet fit easily on high capacity systems, as well as others, using 1/2-inch reducer bushings.
• A 4-inch swing radius allows easy rotation into position inside the tightest furnace vestibules.
• It can be installed at any angle, including vertically between 0–90° from the upright position.
• Its clearly marked, keyed terminal block allows quick attachment of wires and IP/DSI/HSI jumper. A keyed jumper cannot be incorrectly inserted.
• The internal inlet screen blocks contaminants in the gas line from entering the valve.
• Has a -40°F to + 175°F (-40°C to +79°C) temperature range standard.
• Features a standard opening.
There is a cross-reference available online that gives the cross-reference for Honeywell valves, which replace White-Rodgers, Robertshaw and Honeywell valves. The VR8345M- 4302 replaces all of them. Be sure to make note of the footnotes that follow the cross-reference.
In Figure 2, the procedure for applying pipe dope isshown along with the table “NPT Pipe Thread Length in Inches” which is the requirement for NPT (National Pipe Thread) thread length in inches for different size pipe. Teflon tape should not be used at the gas valve as pieces of the tape may break off and end up inside the gas valve.
It should be noted that for Figure 2, the table NPT Pipe Thread Length in Inches applies to all connections of piping to gas valves.
Figure 3 illustrates the requirement for a sediment trap with all gas valve installations. The valve comes with a plug in the pilot tubing outlet for use with DSI and HSI. When using the valve on intermittent pilot, the plug must be removed.
Figure 4 gives a top view of the control for ease of locating inlet and outlet pressure tap, pilot adjustment and pressure regulator adjustment.
Figure 5 shows the proper use of wrenches when installing the valve. These procedures apply to all gas valve installations, not just Honeywell.
Figure 6 shows the installation of pilot tubing into the valve. It is important to always replace the nut and ferrule and use new ones.
Figure 7 shows the installation of the pilot tubing into the valve for intermittent pilot applications.
Figure 8 shows the adapter installation required when using the valve for HSI or DSI applications. The adapter only plugs in one way so you can’t make a mistake. The pilot gas plug must be in place when using the valve on direct burner applications.
This ends Part 1. The next issue will pick-up with universal gas valves operation in various applications. ICM
Part 1 (from May/Jun Indoor Comfort)
This discussion will give some direct application of procedures for troubleshooting hot surface ignition controls. It will not address their use with integrated boiler or furnace controls.
Figure 1 is an example of a very simple application of hot surface ignition using silicon carbide igniters. We will address silicon nitride igniters later in this discussion.
The two igniters from Norton in Table 1 point out the various characteristics of the different igniters they produce. The emphasis here will be on the heating application only using the Norton 201 and 271 igniters, which are 120-volt igniters that have been used extensively for a number of years. Norton introduced mini-igniters in 1988 and my first contact with them was in 1993.
The Norton 401, 24-volt igniter is used with Honeywell Smart Valve Generation I, II and III (SV9540 and SV9640). With the advent of Honeywell Generation III, we see the Norton 601 igniter, which is a 120-volt igniter, used with Smart Valve SV9510/9520 and SV9610/9620.
The Norton 401, 24 volts has a very short warmup time (three seconds) due to it being a silicon-nitride material. It has a low resistance to cold (1–4 ohms) and therefore heats up much more quickly than standard 120-volt silicon-carbide igniters. The Norton 601, 120-
volt igniter also has a short warm-up time (five seconds) with a cold resistance of 50–300 ohms. It should be mentioned here that Norton (Coorstek) also makes Gas Dryer Igniters (the 101) and Gas Range Igniters (the 501).
The igniters shown in Figure 2 are all model 271 17-second warmup time igniters from Norton. The exception is the igniter on the lower right-hand side—the 41-413—which is the igniter used by Carlin for its G3A and G3B power gas conversion burners. It is a 34-second igniter. As you observe the different igniters, the main difference is not the igniter portion itself; they are all basically the same. What is different is the ceramic connector and wiring harness. The wiring harnesses can be cut and wire nuts used if necessary to do so.
Hot Surface Operation
The silicon carbide element can be handled without damage; however, it is better and safer to handle the igniter by the ceramic holder. The myth that the silicon carbide tip cannot be handled because body oils cause contamination is untrue.
On a typical heating system with hot surface ignition, a call for heat (thermostat contacts closed) will send a 24-volt signal to the igniter module. When energized, the module will power-up the igniter. If the module is a pre-purge model, it will delay 15 or 30 seconds before the igniter is activated. On pre-purge models, the module will energize the combustion blower or other relays at the beginning of the cycle.
Once the pre-purge timing is up (if so equipped), the silicon carbide igniter heats up to proper ignition temperature (above 1,800°F) in either 17 or 34 seconds, 20 or 40 seconds for some models, depending on the manufacturer of the module. NOTE: A 17- or 20-second igniter can be used on a 34- or 40-second application, but you could not use a 17- or 20-second module with a 34- or 40-second igniter.
It should be noted here that the igniters are made by Norton (now Coorstek), Carborundum (now Surface Igniter Corp.), Igniter Systems Inc. and some other small companies. For purposes of replacement, the Norton Igniters are distributed by Robertshaw. See 41-400 series for replacement. White Rodgers has its own line of igniters (the 767A series).
At the end of the igniter warm-up period, the gas valve main valve opens. The igniter will remain on for a specific amount of time (seconds) depending on the specific ignition module being used. This “ON” time, or trial for ignition time, can vary depending on the specific ignition module being used. When main burner ignition occurs, the flame is sensed by the igniter (local sense) or by a remote sensor (remote sense). With main burner flame established, the igniter is turned off (120 volts is shut-off to igniter).
NOTE: The burner flame must be detected within the timed trial for ignition. If no flame is detected, the gas main valve is de-energized, shutting off the gas flow. The system may go into lockout, or if it has retry model, it will retry the number of times allocated.
Hot Surface Ignition issues
In some respects, Hot Surface Ignition (HSI) troubleshooting is somewhat more complicated; Figure 3 illustrates this.
• It is not always clear whether you are looking at a pre-purge period or an igniter warm-up period.
• Some of the sequences of operation used with HSI are really complex; if you don’t know what to look for, you may falsely conclude that it is faulty.
• Ignition trials are very short (a few seconds), so sometimes you may have to make measurements fast.
Some preliminary checks can be made on HSI systems that will many times find the problem. The four basic questions that follow can many times pinpoint the problem (see Figures 4-8).
Hot Surface Ignition Troubleshooting
The troubleshooting procedures that follow are more detailed and cover each problem, possible cause, solutions and procedures.
PROBLEM #1: Hot Surface Igniter Does Not Glow Remember to wait for pre-purge time (on models so equipped). Possible causes:
• No main power
• Faulty transformer
• Faulty thermostat
• Faulty limit switch
• Faulty blower interlock switch (pressure switch, combustion blower proving switch)
• Faulty hot surface igniter
• Faulty ignition control or integrated control
SOLUTION #1:
Perform normal system checks of main power, secondary of transformer, etc. With power on and thermostat calling, check voltage at 24V or TH to 24V ground at the module or integrated control. If no 24 volts, check the transformer. Also check other controls in the circuit from transformer to module or integrated control. Check for 120 volts from (L1) to Neutral (L2), check for 120 volts from “IGN” TO “IGN” or on some modules from the HSI terminals. If you have 24 volts to module or integrated control and 120 volts and no 120 or 24 volts out of the module or integrated control, the module or control is faulty. Check the amperage draw of igniter with AMP meter or AMPROBE amperage; it should not exceed 4.75 amps.
PROCEDURE:
1. Perform a visual check of the igniter for signs of damage or cracks. The sleeving over the wire should be examined for chafing, burned portions or cuts in the wire. The connectors should be properly seated and free from oxidation and/or corrosion. Look for “hot spots” on the igniter, as in Figure 9. Also pull on the wires to make sure they have not become disconnected inside the ceramic holder. Observe the igniter during heat up. If a bright, white line across one of the igniter legs is detected, a crack may exist that could cause premature failure. Allow the igniter to cool and perform a resistance test. Additional signs of a crack are an “open” igniter (that shows no continuity when tested) or a buildup of white silica dust around the bright spot. Replace the igniter if you see these cracks.
2. There are several possible causes for repeated igniter failures—one would be high supply voltage. Hot surface igniters can burn out at approximately 132 volts. Even voltages in excess of 125 volts may reduce igniter life. If high voltage is present, request the power company lowers the power.
3. Other causes for igniter failure include drywall dust, fiberglass insulation, sealants or other contaminants that may accumulate on the igniter. In some cases condensate dripping on the igniter causes it to fail. Some sort of protection above the igniter will prevent this from happening again.
4. Furnace or boiler short-cycling, delayed ignition or an over-gassed condition are also contributors to shortened igniter life.
Perform a resistance test on the igniter
PROCEDURE:
The manufacturer recommends performing a simple room temperature resistance (RTR) test after installing the igniter (remember to disconnect the leads to ensure that only the resistance of the igniter is measured). If the RTR is not to specification as shown in Table 1 for igniter Model 201, which is a 34-second warmup time igniter of 45–400 ohms, or the igniter Model 271, which is a 17-second warmup time igniter of 40–75 ohms, then the silicone tip is damaged in some way and should be replaced. When troubleshooting an appliance where the igniter is suspect, the RTR will be higher on a used igniter; the resistance should be no more than double the original resistance at installation. The 201 is 90–800 ohms; the 271 is 80–150 ohms.
PROBLEM #2: Igniter Glows but Main Burner Will Not Light
Possible causes:
• Improper igniter alignment
• Faulty ignition control
• Faulty gas valve
• High inlet pressure (LP gas)
• Polarity reversed
• No earth ground
SOLUTION #2
Make sure gas is available at gas valve. Too high pressure will lock-up the gas valve. Check and make sure polarity is correct. Make sure the igniter is in position (you cannot move the igniter from its designed position). Check for a good earth ground from L1 to the furnace chassis—you should read 120 volts; if not, check and or repair ignition ground wire or ignition control mounting screws. A jumper from ground to gas line should give a good ground. Check for 24 volts to gas valve; if yes and valve does not open, replace valve; if no, replace ignition module.
PROCEDURE:
1. If the igniter is going to be used as a sensor, then make sure the flame is capable of providing a good rectification signal. Make sure that about 3/4″ to 1″ of the flame sensor or igniter sensor is continuously immersed in the flame for the best flame signal. Bend the bracket or the flame sensor and/or relocate the sensor as necessary. Do not relocate an igniter or combination igniter-sensor.
2. Check for excessive (over 1,000°F or 538°C) temperature at the ceramic insulator on the flame sensor. Excessive temperature can cause a short to ground; move the sensor to a cooler location or shield the insulator. Do not relocate an igniter or combination ignitersensor.
3. Check for cracked ceramic insulator, which can cause a short to ground, and replace the sensor if necessary.
a. Make sure that the electrical connections are clean and tight. Replace damaged wire with moisture-resistant No. 18 wire rated for continuous duty up to 105°C (221°F).
PROBLEM# 3: Main Burner Shuts Off Before the Thermostat is Satisfied
Possible causes:
• Improper igniter alignment
• Faulty ignition control
• Contaminated igniter and/or sensor (remote senses)
• Bad burner ground
SOLUTION #3
Check for proper polarity. Check for proper igniter position; make sure proper ignition control is grounded. Check for foreign matter on igniter or sensor. Clean or replace. Check main burner ground by checking continuity between ground and burner. If previous checks are okay, you may need to check the microamps on the system.
Part 2 (from Jul/Aug Indoor Comfort)
When checking the flame signal, it is important to realize that when a hot surface igniter (HSI) is also being used as a sensor, there will be some difficulty in checking the micro-amps. There are several procedures you can follow. In my opinion, the procedure in Figure 1 is the preferred method. It is also important to note the technical bulletin from Norton (Coorstek) points out that the igniter can have a buildup of oxide that can cause it to be a poor sensor.
It has been my observation that when the igniter is used on atmospheric burners, exposing the igniter to whatever contaminants are in the room, the igniter is a poor sensor. Atmospheric burners tend to work a little better when the igniter is used in a sealed combustion chamber that gets its air for combustion from the outdoors.
Direct Sense: The Igniter as a Flame Rod
Sensing through flame rectification, whether “direct” (through the igniter) or “remote” (separate flame rod), involves certain components and variables. The object is to use the ionized particles in the flame (burning gas) to conduct a current and complete an electrical circuit.
The control module initiates an AC signal that is sent out to the igniter. The flame acts as a diode and converts the AC signal to a rectified DC signal. The strength of the signal required to prove flame, and therefore keep the gas valve open, is dependent on the control module and varies from one control manufacturer’s board to another.
Signal strength can be affected by:
• the type of burner,
• the position of the igniter in the flame,
• the age of the igniter,
• the type of gas,
• coating on the igniter and
• any impurities that build up on the system over time.
It is imperative that the flame remains in contact with the burner, and that the burner and control module have the same common ground.
When using the igniter as the sense unit, it is important to remember that as an igniter ages, a thin oxide (Si02) layer is formed on the surface. This is part of the normal aging process of a silicon carbide igniter. As this oxide layer is formed, it actually helps seal the underlying SiC grains and inhibits further rapid oxidation. The silica (silicon oxide) that has formed is a glass, which is an insulator and will diminish the strength of the flame signal that is being sent out. Whether the signal will still be strong enough to keep the valve open as the igniter ages is application-dependent.
Although direct sense can be a very feasible alternative, in the final analysis, it is the responsibility of the Original Equipment Manufacturer’s (OEM) testing to determine if it is a viable solution for the particular application.
Checking microamps with systems using the igniter as a sensor can sometimes be difficult. The problem is distinguishing between the 120 volts AC (VAC) power to get the igniter to glow and then reading the microamps created by the flame to igniter/sensor using the equipment burner as ground.
Figure 1 (previous page) was developed by the author of this article. It includes a list of parts needed to make the switch tester and the wiring to get the switch to work. Figure 3 shows microamp check with a separate sensor.
Hot Surface Igniters Replacements
The distributor for Norton (Coorstek) Igniters is Robertshaw Controls Co. They can be found in the latest Robertshaw Catalogs under the Uni-Line 41-400 catalog series for the Norton (Coorstek) 201 and 271 igniters. It should be pointed out that the igniters that are offered in the catalog are all 17-second warm-up time igniters (Norton 271) with one exception, which is the Norton 201 C (Robertshaw 41-413) used on the Carlin Gas Conversion burner only.
The Mini-igniters from Norton (Norton 601 series) are carried under the Robertshaw catalog series 41-600.
It should be noted that the basic difference between igniters is the ceramic base and the mounting brackets. This makes for some difficulty in using them interchangeably and this is not recommended. It is possible that the mated plug on the lead wires may not match up with the unit being replaced. In that case, the wires can be cut and wire nuts can be used to join the wires.
White Rodgers Control Co. also offers Silicon Carbide Igniters in its F767A series. It should be noted that items in the White Rodgers modules 50E47 series require a special wiring harness as shown in Figure 4.
When replacing White Rodgers with another module system, it requires a wiring change using the special adapter shown in Figure 4, which is included in all the universal module replacement kits, such as Honeywell S8910U.
One of the most helpful things to understand is that these igniters can be cross-referenced with one another in Figure 2 (see page 12). Figure 5 (see page 15) describes White-Rodgers’ silicon carbide HSIs in more depth.
There are several upgrade kits offered by the various manufacturers whose purpose is to convert from a Silicon Carbide Igniter over to a Silicon Nitride Igniter. White Rodgers offers the 21D64-2 Nitride Upgrade Kit. This kit does not need an extra module as the now obsolete 21D64-1 required. You can use the old module to change the igniter.
Honeywell supplies the Q3200U Universal Hot Surface Igniter Kit, designed to provide a robust field service replacement igniter in gas-fired appliances with Norton/St Gobain (Coorstek) 120 VAC silicon carbide HSIs. The Q3200U uses a 120-volt silicon nitride igniter design with long life and high resistance to damage or burnout in the appliance. The kit includes the specially-designed silicon nitride igniter and six different bracket configurations to adapt the igniter to the specific appliance application along with accessory parts to mount and wire the igniter. Clear instructions and application templates are provided to simplify selection of the proper bracket and ease installation of the replacement.
Robertshaw also offers the 41-400N Series, which is a collection of Silicon Nitride Igniters. They are produced by Kyocera and distributed through Robertshaw.
Also from Kyocera and distributed by Robertshaw are the 41-801N, 41-802N and the 41- 803. It is very important to note that these three igniters cannot be used as a flame sensor. A separate flame rod is required, such as Robertshaw 1751-729 (24″ lead) or 1751-749 (72″ lead).
This concludes the two-part presentation on Hot Surface Ignition Troubleshooting. We will cover Universal Electronic Ignition Gas Valves in the next article. 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.
There are only a few differences between gas and oil hydronics. An obvious one is that the burners and fuels involved are different. Controls on older equipment are, however, the same with some exceptions. In this series of articles I want to address the distinctions and how to work with them, along with diagnostics and how to solve problems between these two separate fuel systems. We will briefly address some steam related facts, but our focus will be on forced hot water systems used with gas—both natural and propane.
So far we have been emphasizing older systems in this series. In line with that theme, “New Technologies in Heating” will talk about a little about Modulating/Condensing equipment as gas systems. There are some controls unique to gas, and those are what we’ll want to address.
Above is an example of a typical gas package boiler of the 1950’s up to the present.
Before we get too involved, we need an explanation for the designations of control series. When the heating control industry began coming into its own many years ago, Honeywell was one of the early pioneers. They developed control systems to cover a broad spectrum including gravity warm air systems, steam systems and gravity hot water systems. It became necessary to identify controls for how they were wired and their particular switching action, such as SPST,SPDT, etc. These systems were given “series” numbers, such as series 10 or series 20 and so on. What follows is a brief description of several of the systems involved. A few have been obsolete for some time while others remain with us today. To identify which system you’re working with, you only need look at the first digit in the control number. For example, T105 is series 10, T-26 is series 20, etc. Series 20 controls are no longer available today. There are a few series 10 controls still being produced however, such as the RA 117 stack relay for oil or the R-182 relay. While the series 20 controls are no longer available, the power to open power to close concept continues to be used in some vent dampers, zone valves and modulating motors.
Here is a list of control functions that we want to achieve with Forced Hot Water systems:
• Safety
• Maintain Water Temperature
• Circlate Water
• Maintain Space Temperature
Safety is of course always first priority and should never be circumvented for the sake of comfort. We will be discussing the various controls that help us satisfy these basic control functions.
There are three basic rules of forced hot water systems that simplify our understanding of what can be accomplished. No matter how complex the system, these three rules will remain present consistently. The only exception involves rule three, which does not apply if we do not have a demand for domestic hot water. When the thermostat calls for heat, the burner and circulator turn on together.
This has been the case for many years. As of September 1, 2012, the three basic rules were altered based on a DOE (Department of Energy) rule. In simple terms it states: The boiler looks for 140ºF water temperature or a two minute time limit, whichever comes first, and then fires the burner. If the boiler water is 140ºF or higher then the circulator alone should be running. The boiler burners should only be on when the boiler water is below 140ºF.
• If the boiler goes off while on limit, the circulator will continue to run.
• The domestic Aquastat or Low Limit always has priority over heating.
2012 Residential Boiler Standards
On September 1, 2012, the residential boiler minimum federal efficiency standards went into effect. The standards (set by the Federal Independence & Security Act [EISA] in 2007 then fully implemented Sept. 1, 2012) required residential gas hot water boilers to meet a minimum AFUE of 82%; gas steam boilers, 80%; oil hot water boilers, 84%; and oil steam boilers, 82%.
Most of our new equipment today is classified either as a Category III or IV. A Category III is a system with a positive vent pressure, a stack temperature above 275°F, annual efficiency below 84%, and with the potential for condensing in the flue (usually a stainless steel flue is required). It can’t be vented into a chimney so is typically side-wall vented. It is usually called mid-efficiency equipment.
Category IV also involves a positive pressure in the vent with its stack temperature below 275°F, vented with Poly Pro special venting material. This author does not recommend the use of PVC or CPVC as a vent with equipment, but they can be used as an air intake pipe. By design, these will cause condensation in the heat exchanger. The approach is often called high efficiency equipment with an AFUE above 84%.
Modern forced hot water systems, coupled with 24 volt standing pilot systems, is a system which both modulates and acts as a condensing appliance. Modulation is typically accomplished by varying the combustion air blower speed, which then in conjunction with a negative pressure gas valve causes gas to be premixed with the air varying input to the equipment. Most systems on the residential side have a 5-to-1 turn down ratio. Put another way, a 100,000 BTU piece of equipment would fire from 20,000 on the low end up to 100,000 on the high end with increments in between 40,000, 60,000, and 80,000. Some new equipment now has a ten to one ratio available on residential systems.
Condensation is accomplished by keeping the stack temperature below 275°F and the return water temperature (in the case of boilers) maintained at 140°F or less. The system is designed to allow condensation to take place in the boiler heat exchanger. This, of course, was new allowable on cast iron and steel boilers since it would cause corrosion within the boiler sections.
The following points offer some subjects to consider when looking at installing a Mod/Con to replace your existing, dated boiler with either gas or oil. They are not presented in any particular order, all are important.
•What kind of radiation does the existing system have (baseboard, convectors, radiators)? Most of these are designed to operate above 180°F, so the installer needs to consider whether say in the case of baseboards they are designed to give 600 BTUs per lineal foot at 180°, for example. Will a temperature below 140° adequately heat the dwelling? More baseboards may need to be added in order to meet the room BTU heat loss.
•Can this type of system be used on an old gravity hot water system? With some piping changes it can be done and definitely requires outdoor reset and mixing controls.
•Water temperatures become important as some manufacturers have a high limit of approximately 165°F as a maximum temp on their boilers.
•Did heat loss occur? If so, do not trust the previous inputs on older equipment.
•Piping changes to primary secondary, of a low loss header.
•Water temperature mixing certainly in the case of domestic hot water applications.
•Complexity of control systems. It’s worthwhile to keep things as simple as you can.
•Make sure you know that annual maintenance is required on these systems. These are not your old gas boilers, which required very little maintenance. Let the customer know about annual requirements and their cost.
•What is the preferred type of boiler heat exchanger? Stainless steel, cast aluminum, cast iron, something else? All of these are available from different manufacturers for use on condensing equipment.
•How is domestic hot water going to be supplied? On demand, indirect, or storage?
•The history on the new equipment as to the performance, problems, etc. ICM
There are not a lot of differences between gas and oil hydronics. The obvious one is the burners and fuels are different. The controls, however, are typically the same with some exceptions. I want to, in this series of articles, address the differences and how to work with them. In addition to the diagnosis and solving of problems on the two different fuel systems, we will briefly address some steam related facts. However, our emphasis will be on Forced Hot Water systems used on gas both Natural and Propane gas.
We will be emphasizing the older systems and not in this series get into Modulating/Condensing equipment. I want to address controls that are unique to gas. Below is an example of a typical gas package boiler of the 1950s still used in the present.
Pumping Away
Systems work better when the compression tank is connected on the suction side of the pump. This is called the “Point of No Pressure Change.” This is the way commercial systems have been installed for years. This typically means that the circulator is installed pumping away from the boiler and toward the systems.
The idea has in recent years caught on with residential and small commercial piping. It was probably not done in the past because no one ever gave people a good reason to change, but now there is a good reason. Just look at all the changes that circulators have gone through over the past few years. These new circulators are smaller and run at higher speeds and higher heads.
That makes a difference in the way the system operates. We have seen so much of a difference, in fact, that we see a brand-new opportunity for you.
When a circulator pumps away from a compression tank (expansion tank), all the circulator’s pressure appears as an increase out in the system. This sudden increase in pressure helps move air out of the radiators. Start-up becomes much easier, and, usually, there are fewer air-related problems from that day on.
On the other hand, when you pump toward a compression tank (typically, when the pump is on the return side of the boiler), the circulator’s pressure appears as a drop in pressure on the circulator’s inlet side.
If you’ve ever piped a feed valve into the inlet side of a circulator on the return side of a boiler, you’ve seen this drop in pressure. The feed valve opens every time the circulator comes on. It can be a real problem.
This sudden drop in system pressure also makes it harder to get the air out of the radiators. System start-up is tougher (especially on one-pipe systems with venturi-type fittings) and, in some cases, air can actually be sucked into the system through the air vents.
No one really noticed this problem with the older circulators, but nowadays, many residential systems are using small, high-speed circulators. These circulators, because of the higher heads they produce, can help you remove system air—if you install them pumping away from the compression tank and toward the system, or they can work against you.
When you install them pumping toward the compression tank, they will drop the system pressure on their inlet side (as much as six psig) every time they come on. That sudden drop in pressure will expand the trapped air bubbles up in the radiators, making it even more difficult to get air out of the system.
Have you ever noticed how it always seems to be those last couple of convectors, the ones closest to the return, which give you the biggest problem on start-up? Now you know why.
Why not use this pressure phenomenon to your advantage? Pump the supply side. The system will work a lot better and you may be amazed at the results. We say this even as we recognize that pumps installed on the return side have worked for years. They’ve even become a tradition. Most of the drawings published over the years show the pumps on the return side and with the low-head pumps, this usually is not a problem. However in light of today’s high-head circulators, we’ve become convinced that your systems will work much better and start up a lot easier if you take this fresh approach of pumping away. It’s good to question habit and tradition from time to time.
Some examples are illustrated:
Below is an example of pumping away with circulator on the supply side, which is the preferred method. The circulator can however be placed on the return and still allow for pumping away from point of no pressure change.
Control Systems
As we go over different controls, all of them will fall into some category of what part of the system they function in or control. This is an example of some that in particular are used in hydronic systems in particular. The listing includes controls also used on forced warm air so that we may have some point of reference.
1. Primary Controls (loads)
A. Is the control that is being controlled by the thermostat or controller.
B. Require power for their operation in:
(1) Gas Valves
(2) Relays
(3) Zone Valves
(4) Zone Dampers
(5) Flue Dampers
2. Operators (operate primary controls) (switches)
A. Thermostat
B. Aquastat
C. Pressuretrol
3. Secondary Controls
A. Pressuretrol (2 lbs off .5 lb on (steam) (hot water
and steam)
B. Low water cut off
C. High limit (warm air) (200°F)
D. High limit (hot water)
E. Low limit
F. Fan Control Normally Open (Closes on a
temperature rise)
G. Reverse acting control (pump aquastat, circulator
control)
4. Loads
A. Relay coil
B. Motors
C. Transformers (primary load) (secondary source)
When it comes to setting temperatures for forced hot water conventional systems, the Incorporation by Reference (IBR) handbook suggest settings follow.
Settings for different systems
STEAM: Pressuretrol: 2 lbs. off–.5 lb. on (on normal household jobs)
VAPOR: Vaporstat: 8 oz. off–2 oz. on (unless engineer gives different setting)
FORCED WARM AIR: Combination fan and limit control
Limit: 200°
Fan on: 125°
Fan off: 110°
(if separate controls, set accordingly)
GRAVITY WARM AIR: Airstat Limit
control: 250°
GRAVITY HOT WATER: Aquastat Limit
control: 140°–150°
FORCED HOT WATER: High Limit control: 185°
(for radiators) 200° (for convectors)
210°–215° (baseboard radiation)
Low limit control: 150°
Circulator control: 120°–125°
(If there is a combination control with low limit and
reverse on the same setting, set the low limit to 150°and the differential to 25°).
AUXILLARY LIMITS
STEAM: Pressuretrol: 2 lbs off–.5 lb on.
Auxiliary pressuretrol:14 lbs off–
(set cut in to nine and differential to five) 9 lbs on.
HOT WATER: High limit 180°
Auxiliary high limit 220°
Thanks to Dan Holohan for the information on pumping away. Contact him at HeatingHelp.com.
