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Hot water heating circulators or circulator pumps: install, troubleshoot, repair advice: this article series discusses Circulator Pumps: how to find, inspect, diagnose, and repair problems with Hot Water Heating System Circulator Pumps or circulator pump relay switches and controls.
This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.
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Heating circulator pumps or "zone circulators" are used to force hot water from the heating boiler through radianting devices such as hot water baseboards or radiators. The circulator is switched on as needed or in some designs may be wired to run continuously.
Our photo at left of a red B&G heating circulator pump shows equipment more than twenty years old and still spinning along nicely. Proper installation, protection from leaks, and lubrication at annual service can give a long circulator life. Poor maintenance or improper installation can give less happy results.
[Click to enlarge any image]
After a brief introduction we describe what goes wrong (or how to get things to go right with heating zone circulator pumps. We also link to related articles for circulator choices, installation, troubleshooting, repair or replacement. Also see Checks for Circulator Operation.
Hot water may be circulated throughout multiple zones using a single circulator pump and individual zone flow control valves, or each heating zone may be built with its own individual circulator pump. Either approach to individual heating zone control can work just fine - using zone valves or using individual circulators.
Our photo above shows a single circulator system (no zone valves are in the photo - this may be a single-zone heat system) while at left our photograph shows a three-zone heating system with three B&G circulators in a home in Two Harbors, MN. You'll notice that one of the circulators has been replaced with a newer Bell & Gossett Circulator SLC-30.
Arguing whether multiple circulators or multiple zone valves is better is like arguing religion. Some heating contractors prefer using individual circulator pumps, one per zone, perhaps because they recall the history of unreliable zone valves which tended to clog or jam in some models by some manufacturers.
The "zone valve" gang retort that modern heating zone valves are as reliable or more reliable than [some models of] heating circulator pumps and that a zone valve costs a lot less. And adding zone control to an existing heating system may be less costly by adding a zone valve than by adding a circulator pump.
The heating system circulator pump, such as the trio of pumps shown at the top of this page, is used to move hot water from the heating boiler out through one or more loops of piping in a building, through heating devices such as radiators, heating baseboards, or convector units, then through return piping back to the heating boiler. When the water temperature drops to a pre-set level the heating boiler will re-heat the water.
[Click to enlarge any image]
The circulator relay is an electrical switch which, in response to a request for heat from a thermostat, turns on the circulator pump.
Some heating systems use a single circulator to move hot water through the building's heating devices. In a one-circulator system, the building may still divide its heat into various zones or sub-areas of individual heat control, by using either individual radiators in rooms or perhaps by using electrically controlled zone valves which open and close flow of hot water through sub-loops in the building heating piping.
Some heating systems use multiple circulators to provide heat to individual building areas or "zones". In this case each heating zone will have its own thermostat which, acting as a low-voltage "heat on-off switch" will turn on individual circulator pumps when heat is desired in that zone.
Less common are mixed heating zone systems in which multiple circulators are used but one or more of the circulators feeds a heating water pipe which is subsequently divided into additional sub-zones of heat control, each sub-zone being controlled by a zone valve.
Before assuming the heating system is not working when the thermostat is calling for heat, feel the radiators or baseboards to see if they are getting hot. On a call for heat at the thermostat, if the heating boiler is already hot (above the lower limit or cut-in temperature) then the circulator should turn on and move hot water to the baseboards or radiators.
Only after the boiler temperature drops below the cut-in temperature will the heating boiler turn on to re-heat the water. The connection between the thermostat and the heating boiler turning on or off is indirect. On most heating systems the thermostat turns the circulator pump on or off and the temperature of the heating water turns the heating boiler on or off.
If the boiler runs but the heating baseboard or radiators in an area do not get hot, the problem could be
If the heating boiler itself if does not turn on in a response to a call for heat see NO HEAT - BOILER.
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Frequently Asked Questions (FAQs) about hot water heating circulator pumps & relays: installation, troubleshooting, repair
(Oct 23, 2011) Mary said:
Is it normal for a pump to stay on all the time? We have a new system installed and the pump wont go off at all. Thermostat set to 70 and burning smokeless egss.
(June 5, 2012) Greg said:
Didn't see anything listed above for this but it seems our hear came on last night and went off, but apparently the circulator was still running 2 hours later. So, we decided to turn it off at the switch. Any ideas what could cause this to happen? Before I left for work, i turned the switch back on, i heard the vent open on the pipe leading to the chimney then the furnace kicked on. In less than 5 minutes the furnace turned off but the circulator kept running.
When the day's are warm and I turn off the heat do I shut the circulator pump off also?
Chris, when you turn off the heating system at its power switch your circulator pump should shut off on its own. If it does not then there is a wiring or control SNAFU that we need to discuss.
Normally you shouldn't have to do even that. If house temperatures are above the thermostat set temperature the thermostat will not call for heat and the heating system as well as its circulator should not run. If you are seeing something else happening let's figure that out. Tell me.
4/21/2014 Dan, the heat was turned off this past Saturday. The circulator pump would still turn on though the heat was switched off on the thermostat. My centralized air and heat are on the one thermostat so I need to turn off heat to power on the central air unit.
Chris, you don't say where you are located; in some areas including much of Canada the hydronic heating system practice is to run the circulators continuously and allow the thermostat to simply turn the boiler on and off - an approach that tends to give more even heat and reduces the risk of heating line freeze-up in a colder climate. In the U.S. installers usually wire the thermostat to turn on the circulator and allow the boiler temperature to turn the burner on and off.
When you switch from HEAT to COOL mode on your system it would make sense for the circulator to turn off as well as your boiler. If it's not doing that we need to look at how your thermostat and circulator are wired and controlled. If you're one of the Canadian type installations you will want to find the power switch to the circulator pump and just flip that off as well, remembering that in the fall you'll need to turn it back on.
Part of the answer to this question depends on what heating system installation practices are common in your area. In the U.S. some areas a hydronic heating system is wired so that the thermostat simply turns the circulator pump on - ostensibly to move hot water from the boiler to the heated area.
In turn it's the temperature of the water in the system that, monitored by the boilers aquastat, turns the burner on and off.
If a problem at the heating boiler prevents its operation (such as no oil, or off on safety reset), the circulator may just keep spinnining away but no heat arrives in the heated area.
Take a look at the boiler to see why it's not running, starting at DIAGNOSE & FIX HEATING PROBLEMS-BOILER
(Oct 29, 2011) Mark said:
I have a Weil-McLain furnace/boiler model no. CGM-5-PI. I just turned on the heat system two days ago and I noticed the circulator pump is not spinning its motor. I bleed all the valves on all the radiators. The two upper levels get heat on the radiators, but the one on the entrance level is not getting heat. Is this caused by the pump not working? Is there any danger/risk of running the heat with the circulatory pump not working? How much would it cost to replace the circulatory pump? Any information would be helpful. Thanks.
(Nov 24, 2012) annonymous said:
circulator pump goes on when heat called, runs thru cycle, but doesn't come again.....burners come on,but not circulator which in turn system goes off
Mark if the circulator pump won't start when the boiler temperature is sufficently high that it should, you would check:
1. the thermostat is calling for heat and the room temperature is below the thermostat set temperature
2. the boiler temperature is above the circulator cut-in temperature controlled by the aquastat
3. the circulator pump has power
4. the circulator relay has power and is switched "in" or callling for the circulator to run
5. the circulator pump itself is not damaged, jammed, frozen
Question: should the circulator pump come on right away?
(Oct 27, 2011) Steve said:
My daughter bought a house with hot water heat. I bled the radiators, oiled the circulator pump and turned up the thermastat in order to check the operation. The circulator pump did not start to opereate until the boiler temp read 150 degrees. The pump is hooked up to an aquastat (the thermastat located against the pipe exiting the boiler) which is set at 140 degrees. The radiators do heat up. Shouldn't the pump come on right away?
Steve, on a very common hot water heating system installation the aquastat is a combination control that includes a HI LO and DIFF setting - the LO and DIFF settings control the boiler when no heat is being called for and maintain heat in the boiler to provide domestic hot water through a tankless coil - that might not even be present or not in use on some installations. If that general control and approach are in use on your system and if your system is hooked up in the manner typically used in the U.S. (not in Canada) the circulator won't turn on until the temperature is sufficiently high in the boiler.
My furnace's circulator pump has been running in short bursts only lately, as opposed to full length cycles. It's a gas-fired hydronic system, a high efficient one w/ a Peerless Pinacle furnace. never experienced this before.Do you have any ideas? - mark4man 12/5/2012
(Dec 29, 2011) Richard VanMetter said:
When my thermostat calls for heat the gas comes on and the internal temperature of the furnace increases (approaching 250 degrees) but the circulator pump only runs intermittently (5 seconds on 30 seconds or more off). Shouldn't it run constantly once the internal temperature of the furnace is adequate?
(Nov 11, 2012) Anonymous said:
Hi i have an open fire with back boiler the pump is beside the back boiler and the thermostat is on
My circulator pump turns on then shuts off in 3-4 sec. could tis be a switch?
First I'd check for a bad circulator control relay or possibly a thermostat wire that is intermittently shorting together. Occasionally a bad thermostat can also cause intermittent on-off calls for heat that can lead to odd circulator behavior.
A second set of possibilities might be a circulator pump that is binding or failing.
A short on-off circulator cycle such as you describe sounds to me like a wiring (damaged wire), thermostat, or circulator relay problem.
Phil, I wonder if there is a bad relay in the circulator control, or an intermittent short of the thermostat wires. Try disconnecting the thermostat entirely to rule out that source. Then connect the red and white heat wires (or equivalent if yours are different) that calls for heat. Connected = heat on. Disconnected = heat off.
(Feb 8, 2012) Kelly said:
Can you continue to run the boiler if the circulating pump is not working properly? The house is heating but I'm concerned about how safe this is. The pump tries to turn on but is not and i believe it may be the coupler and will have someone out to fix it but in the meantime; i just don't want to cause any more damage by keeping the heat on.. it's only 25 deg's today so i'm hoping it's not dangerous.
In general (which means we don't know a thing about your heating system so this may be wrong for you), heating boilers are controlled by one or more temperature-sensing devices - aquastats - as well as other safety controls. If a circulator pump is not working but the boiler is heating up, the boiler should not get hotter than the upper safety limit set by its HI LIMIT control.
Hot water will still circulate in some heating systems that use circulator pumps or even zone valves, even if the circulator pump is not working. Hot water will rise out of the boiler by convection and cooler water will return to the boiler's return side by the same process
In some heating systems one can over-ride a check valve at the boiler by manually turning a lever, and similarly one can manually open some heating zone valves.
The result is that heat will be delivered to the building by convection - more slowly than if the circulator were running - but still effectively.
In fact more than once I found this situation in homes that had hot water heat but no working circulator. The home would heat to a satisfactory temperature, but more slowly than occupants might have preferred.
This is also a stop-gap or backup method of keeping a building heated while waiting to replace or repair the circulator or circulator relay.
Question: circulator mounting position vs system pressure
(Mar 2, 2012) Ken said:
I'm seeing pictures of products installed incorrectly with no mention that they are wrong. You should only post pictures of the items that your talking about that are correctly installed. The circulators at the top with the motor in the up position is incorrect unless your are running over 20lb's of system pressure, there are also pictures of oil filters mounted right at the burner on other pages which doesn't allow enough distance for the oil to stablize before enturing the pump. There is more, but enough. Please upgrade your pictures.
Thanks Ken, interesting points, though in some cases lacking authoritative citation of expert sources. If you can give me a source citation for oil stabilization problems, for example, we'd be very glad to add that to our information. The photos shown throughout these heating articles are indeed from "real world" rather than theoretical installations and are indeed deserving of comments about good and bad practices.
Question: how do we control hot water flow when using multiple circulator pumps?
July 3, 2012) Anonymous said:
when using pumps for zoning,what stops the water from enterning the other zones
Anon: the flow-control valve, a check valve usually found at the boiler hot water riser pipe(s), prevents water from circulating through zone piping until the circulator for that zone begins to spin - causing a more significant pressure difference across the zone.
Question: adding zone valves and sub-zones on a hot water heat system
(July 16, 2012) kenny said:
if i decide to add a zone valve to my boiler do i have to hook it up to the relay on the boiler
In this installation a thermostat operates the zone valve on a call for heat, causing the zone valve to open to allow hot water to flow thorugh that zone piping loop. Then the zone valve's end-switch that closes to turn on the circulator relay.
Kenny - as you'll see in the wiring instructions for your zone valve, the thermostat causes a low voltage motor in the zone valve to OPEN the valve so that hot water can flow into the zone. When the valve is fully open, an "end switch" in turn talks to the circulator relay to tell it to start the boiler's circulator pump.
Question: reader comments on multiple circulators vs. multiple zone valves for heating zone control
(Aug 17, 2012) Barney said:
I have tried both multi pumps and motorised valves and I would like to make a few points.
Firstly, the cost of modern 60-30 or 50-30 pumps are not that much more costly than the more popular motorised valves. When you consider the failure rate of the seemingly most popular Honeywell and their copies (normally cheaper)motorised valves the multi-pump approach is probably cheaper.
This is because of the Honeywell type design which depends on a synchronous motor running to hold the valve open and eventually the synchronous motor fails. They are not teribly expensive but a hastle to change and if you can't do it yourself it costs a plumber/heating man. There are better designs such as the Satchwell but are still very expensive. I use Grundfos pumps and in particular the Alpha 2 model.
It is surpurb. My system uses 5 Alpha 2's 60-30 pumps where I have removed all the motorized valves. I have bought some on mine on Ebay which are new and work fine.
Another point, many heating engineers are full of s--t in saying you have to use a larger pump on large systems. I have talked to Grunfos technical people and as long as the pump is able to meet the water volume load the smaller pumps are fine. I use the Alpha 2 rather than the Alpha 2L pump becaause of the display showing the Load being taken in Watts. My circuits are running at between 9 and 12 watts which over a period of time represents considerable savings in electricity over the lower cost and more older 35 watt cheaper traditional model. A couple more points to answer some of the comments made and questions.
No, you do not have to use a relay as most if not all 230 volt thermostats can cope with the small current requirements including startup currents of most modern pums like the Alpha 2.
Anaymous is wondering about water backing up into the other zones. I wondered also and installed at the end of each loop a non-return valve. Very simple device and very cheap from BES in the U.K. Hope this helps somebody!
Question: circulator pump cost
(Dec 28, 2012) Mary Tilma said:
What is the average price of a circulator pump?
Mary, Grundfoss & Bell & Gossett heating zone circulator pumps are typically in the range of $100. to $300. depending on the pump model.
Question: fan convector unit blowing cool air
(Feb 2, 2013) Gerry said:
When my fan comes on, the boiler temp gauge is showing 180. Right by the gauge is a limit control (clamped onto the pipe) which is set at 180. The temp control on the boiler is at 180. I have no diff control. It is a 11 yr old Weil Mclain boiler with a coil in the duct work. Which limit control is the hi and which is the low one? When the fan comes on, there is no circulation of hot water through the pipe into the coil. It is warm but slowly cools.
As soon as the burner comes on, the gauge shows 160. and hot water starts circulating. I did have a service person put a new pressure gauge on, he then set the temp gauge on the boiler at about 210, and left the one on the pipe at 180, then he put the pressure up to around 24 psi. It was originally at 15. What should the limit controls be set at and which one is which? The fan runs blowing cool air until the burner starts, then there is heat. I'm going crazy trying to figure this out. Help!!!!
Gerry, if the fan convector you describe is not receiving hot water indeed it'll just blow cool air. Setting the heating boiler HI LIMIT up to 210, as your service tech tried, sounds like a band-aid approach that's unreliable and risks dumping the pressure-relief valve. S/he may have been trying to force hot water through the system hoping that air bleeders and vents will allow self-correction of an air bound system
f the circulator pump is running but hot water is not moving through the piping you need to check the diagnostics at AIR-BOUND HEATING SYSTEMS.
Question: direction of hot water flow through the circulator pump and piping loop
(Feb 18, 2013) greg said:
I am installing a circulator pump on an outdoor wood boiler I have been told that some stove have been installed to pull water from toward the bottom and returning on top and also the other way around. what is your advise?
Greg I don't know quite what's the design of your system. In general, some installers like to put the circulator pump on the return side of the hot water piping loop, figuring that by running the cooler water rather than the hotter water through the pump assembly it will last longer.
(Jan 23, 2014) Andrea said:
Can a poorly functioning circulator pump cause an insufficient heat supply? I have a tenant who can't get his apartment to heat up to where he's setting his thermostat. For example, we currently have his thermostat set at 72 degrees & it's only 64 in the apartment & the problem gets worse the colder it is outside. I had a plumber do a heat loss calculation & there is enough baseboard to heat the space sufficiently. We checked the fins on the baseboards & they are in good, clean condition. We also replaced the thermostat today just to see what would happen & that hasn't helped either. Any other advice or suggestions? Thank you!
(Jan 26, 2014) Heidi said:
The heat coming from our baseboards is not enough and the boiler goes off even thought the temperature is nowhere near the thermostat set point. The temperature of the water returning to the boiler is 150, even when the aquastat is set to 220. I am trying to tell if this is a pump problem or an aquastat problem. If the water coming from the valve below the pump is 150 degrees (despite much higher aquastat setting), could the problem still be the pump? The circulator pump feels hot, and there is no visible damage. The pipe at the outlet side of the pump is as hot at the inlet side. Thanks!
(Sept 10, 2011) Melissa Paige Leigh said:
I have repalced the well assembly and relief valve in my hot water tank. Digital stat turns in, kicks burner on then burner shuts off and does not heat water. Any idean what the problem could be.. I bled the burner and ran hot water faucets to ourge any air, oil tank is 3/4 full . Have Taco circulator on supply to hot water tank.
Melissa, this doesn't sound like a circulator problem - in which case you'd want to start diagnosing the trouble at DIAGNOSE & FIX HEATING PROBLEMS-BOILER.
But I make this exception: if the circulator pump is damaged or its relay is not kicking on the pump, the thermostat would call for heat, the boiler would heat up, but as the circulator is idle, no hot water would circulate into the occupied space. In that situation the burner would indeed turn off when the boiler reached its HI LIMIT setting.
Certainly; if the circulator pump is not actually circulating hot water through the heating zone then the zone may still get some heat - by natural convection (hot water rises in the pipes) - but much less than if the circulator were running.
I'm betting that those pipes are tepid and if you feel along them you'll get to an area where they are downright cold.
If that's the case then the system is probably air-bound. Your plumber or heating tech will need to confirm that theory and then purge air from the system.
You need to check the diagnostics at AIR-BOUND HEATING SYSTEMS.
What you pose makes some sense to me except that in my experience circulator pumps usually either move water or they don't, excepting further that some circulator pump models provide for variable circulation speeds. When I hear that heat is inadequate and that people are replacing the thermostat, that sounds as if we're shooting in the dark.
Your system might be partly air-bound. In some hot water piping systems air can lurk along horizontal piping runs occupying part of the volume of the pipe interior without totally blocking hot water flow. A result would be reduced hot water flow volume and cooler radiators or baseboards.
this is a pretty interesting question. We'd like to know *why* the baseboards don't seem as hot as you want. Usually the problem is a reduced water flow-rate. Slower flowing water (say from a partly-shut valve) means that the room is losing heat fast enough that the baseboards just don't give enough heat to keep up;
Other less common causes: long heating pipe runs through un-heated spaces, damaged circulator impeller, or improperly set heating controls, or thermostat.
I would start by taking a close look at as much of the piping as you can follow by eye and hand. Start at the boiler, follow hot water out of the boiler through the zone valve (if one is installed) or circulator (though we prefer to see the circ on the return side not the supply side of the pipe loop).
Look for a manual valve (a handle or gate valve on the heating pipe) that regulates flow, or look for a little flow control valve and see if it is partly shut. Some HVAC manufacturers call these flow-balancing valves - harder to spot than a valve with a handle, you'll see a fitting on the zone piping (usually near the boiler) with a flat-blade screwdriver slot. If the slot is turned parallel to the pipe the valve is wide open. But if it's at an angle it's partly shut. If it's at right angles to the pipe it's fully closed.
I'll find a photo of this device, post it online and add a comment here pointing to the image.
(Mar 2, 2014) Jared said:
why does heat come out of zones where thermostats are not calling for heat?
Jared, usually the problem you describe is traced to a check valve malfunction at the heating boiler or at the circulator pump (depending on what equipment is installed). Hot water can circulate by natural convection (warm water rises in pipes, cold water falls) even when the circulator is off.
Question: heating system noises, or noises when heat is turned off
(Oct 13, 2012) zena123 said:
Help, please ! Central heating system is turned off. However, an unpleasant hum comes from central htg. boiler. When elec. is turned off at consumer unit, humming ceases. Any ideas gratefully received. Tx.
(Oct 29, 2012) Jim said:
When circulator pump turns off, there are 4 pairs of bang-bang, which seem loudest at expansion tank. Draining expansion did not change. Heating and other operation is OK. I suspect, and will replace, the coupler between electric motor and impeller.
(Jan 10, 2013) Anonymous said:
I hear trickling water on one of my baseboard on my top floor everytime the heat starts to work. It goes away after awhile. I bleed that baseboard and it still trickles.
(Mar 13, 2014) Steveo said:
I have a squeeking noise that only happens early in the day and then again at night...it is coming from the water-out pipes (hot) and the sound "goes away"...I'm really confused. The pump's coupling was changed this season and it was oiled...any ideas??
I'd try to track the noise to location as well as by whether or not equipment is running or not. It could be an expansion/contraction of piping moving through a tight opening as temperatures change.
See the heating noise diagnostics listed at HEATING SYSTEM NOISES
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