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Multiple heating zones with individual circulators (C) Daniel FriedmanCirculating Pump Won't Run
Diagnose & fix circulator pumps that won't start & run in response to a call for heat

Heating zone circulator pump won't start or seems stuck: how to diagnose & fix a heating zone circulator that will not run when it should.

This article series describes how to diagnose & fix circulator pump problems on hot water or hydronic heating systems.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Diagnose Stuck or "Dead" Zone Circulators on Hot Water Heating Systems

Older model B&G Red Circulator Pump (C) Daniel FriedmanReader question: My heating zone circulator won't start-up

(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

Reply: Six Steps in Diagnosing a Heating Circulator Pump that Is Not Working

Mark

In answer to your cost question, Grundfoss & Bell & Gossett heating zone circulator pumps are typically in the range of $100. to $300. depending on the pump model.

If the circulator pump won't start when the boiler temperature is sufficently high that it should, you would check the following:

1. Check that the thermostat is calling for heat and the room temperature is below the thermostat set temperature. First set the room thermostat all the way "up" so we know it's set above the room temperature.

2. Check that the boiler temperature is above the circulator cut-in temperature controlled by the aquastat. Take a look at the boiler temperature on the gauge on the boiler and take a look

at the AQUASTAT HI LO DIFF SETTINGS

- or just check out

this AQUASTAT OPERATING CHART

where you'll see that the temperature has to be above the LO setting for circulator to run. (Otherwise it's locked out on most systems).

3. Check the circulator relay has power and is switched "in" or callling for the circulator to run.

There will be a relay switch either in the aquastat on your boiler or one or more additional circulator relays controlling additional circulator pumps if there is more than one circulator pump. The thermostat wires act as a simple "on-off" switch, connecting to the circultor relay in the aquastat or in the separate circulator relay.

If we suspect that the thermostat is not working we disconnect the two T T wires at the relay or aquastat, then jump the two T T terminals together. This is exactly the same as what would happen if the thermostat is calling for heat.

When the TT wires are jumpered OR the thermostat is calling for heat, the circulator relay should "pull in", switching on 120VAC to the circulator pump itself.

Some old timers push down on the circulator relay - if it clicks on (and the pump runs) then the relay was not being pulled in by the thermostat (switch) OR the relay itself has failed.

Watch out: exposing or touching live electrical wiring connections can shock or kill you. If you do not know how to make these tests safely don't try it: call for help from a trained professional.

See CIRCULATOR PUMP RELAYS & OTHER CONTROLS for details.

4. Check that the circulator pump is getting electrical power

When the circulator relay is switching on 120VAC to the circulator pump itself we should see 120VAC at the power terminals at the circulator pump.

Watch out: exposing or touching live electrical wiring connections can shock or kill you. If you do not know how to make these tests safely don't try it: call for help from a trained professional.

5. Check that the circulator pump itself runs and is not damaged, jammed, frozen - how to tell if the circulator is running - below we give seven ways to test a circulator pump to see if it's running and if it's pumping.

If the circulator pump has power but the pump is not spinning then there is an internal problem in the circulator pump or pump motor or its impelller.

Some circulator pumps make enough noise and vibration that it's obvious if the pump is running. Some circulator pump models such as the older B&G red circulator pumps actually have exposed linkages between the electric motor and the circulator impeller assembly. You can actually see the link spinning.

Watch out: it is difficult to tell if some other circulator pumps are actually running: a TACO brand circulator is often virtually silent - even feeling its vibration can be tough.

Signs of a "dead" or "dying" hot water heat circulator pump:

6. If the circulator pump runs and the boiler is hot but the radiators or baseboards do not get hot the system may be air-bound:

See COLD HEATING BASEBOARD / RADIATOR REPAIR

How To Tell If A Heating Boiler Circulator Pump Is Working

Overheated circulator pump motor, cool zone piping suggests that the circulator motor has failed (C) InspectApedia.com DJFPhoto: when the zone served by this circulator was ice cold we confirmed that the circultor relay had pulled-in, that electrical power was delivered to the circulator motor, and that the zone was (probably) not air-bound.

[Click to enlarge any image]

After leaving the thermostat and circulator relay "on" - calling for heat - overnight, the circulator motor itself was very hot, but the zone piping on the outlet side of the circulator, just a few feet away, was cool.

The circulator motor was not able to run. It's possible that replacing the circulator motor's start/run capacitor would have got it spinning, but the service technician felt it safer to replace teh whole circulator motor assembly. That fixed the "no heat" problem.

  1. Feel the heating pipes: If your heating boiler is hot and the circulator is running, you should feel high temperatures in the heating pipes entering and leaving the circulator.

    If just a few feet from the circulator's output side the pipes are cold, most-likely the circulator is not pushing hot water. (Also see our air bound heating warning at the end of these notes).
  2. Listen to the heating pipes: Close a zone service valve part-way. If there is a service valve on either end of the zone piping for the circulator in question, slowly close the valve.

    If the zone shutoff valve is actually working (sometimes a gate valve handle spins but does not raise or lower the gate), as the valve closes and the restriction of the zone flow increases you should hear an increase or at least a change in the flow noise in the zone.

    If there is no noise change then no heating water is flowing.
  3. Feel the circulator motor: Also feel the circulator pump motor itself.

    If the motor is scalding hot to the touch and the heating pipes are noticeably cooler then the motor is overheating and is most-likely damaged.
  4. Listen to the circulator motor: I sometimes use a mechanic's stethoscope to listen to the motor on the circulator pump. No noise, pump not running. Screaming noise, failing bearing.
  5. Measure circulator pump current draw: I often use a DMM or VOM to measure the current drawn by the circulator pump.

    If the current drawn is well above (more than 10% above) the FLA given on the circulator pump motor data tag then I suspect the motor is binding or damaged.

    If the current drawn is well below the FLA (less than 10% of the FLA) given on the data tag then I suspect the motor is spinning with so little resistance that it is not moving the actual impeller assembly. A linkage or impeller shaft has broken.
  6. Check or replace the circulator motor start/run capacitor: or test the capacitor if you suspect the motor is not starting.

    See TEST a MOTOR START or RUN CAPACITOR or just swap in a new cap of the same rating.
  7. Cute little motor test tools: I've read that there are specialty tools (a magnet in a sight-glass) that can tell you if an electric motor is spinning. If anyone has one of these send us a photo using the comment box and its picture frame icon at the bottom of this page.

    At ELECTRIC MOTOR DIAGNOSTIC GUIDE we explain how to test electric motors

    At DMM DIGITAL MULTIMETER HOW TO USE - and also

    at DMMs VOMs SAFE USE OF we describe how to use a digital multimeter to make checks for power and continuity.

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-04-22 by (mod) - successful repair of B&G Circulator pump that would not start

@Denys Picard,

Shown here: a newer 1/12 HP, Series 100 NFI Circulator Pump from B&G

[Click to enlarge any image]

Good going on repairing your B&G circulator pump.

When a circulator bearing fails in my OPINION the most-likely cause is inadequate lubrication,
but
I have also seen recurrent bearing failures at circulator pumps that were not properly mounted and aligned.

A simple, low-tech test I was taught was with the motor disassembled and safely OFF, we'd see if there was end-play at the motor shaft - at either end but especially at the drive end. A side wobble or even a back-and-forth along the axis of the drive shaft play that was noticeable was often a sign of a failing bearing.

It's more-difficult to make that assessment of the bearings in the actual circulator pumping assembly on those older B&G circulators.

I inspected a heating repair job years ago (in NY) where occupants complained that their B&G circulators were not lasting even through one heating season.

In the basement over behind the boiler was literally a pile of dead circulator assemblies.

The repair tech would not have replaced a bearing but rather (saving hundreds of dollars in labor) just swapped in a new circulator motor + actual circulator assembly.

We found that the mounting brackets used to support the circulator at this site were askew - mis-aligned - so that every new installation of a circulator subjected it to a downwards force between the motor output shaft and the circulator pump assembly - killing one after another.

On 2021-04-19 by Denys Picard

Dan, while I was waiting for your reply from my second diagnostic (with pictures) I sent yesterday after your directions, I tired to in stall the bearing assembly to the moor again. And guess what it worked.
Now, some explanations:

1. The pictures yesterday showed the front of the motor and the cement block with some oil...I forgot to tell you that when I pulled the motor (and assembly) on Saturday, I had forgot to put the heat call to off, so when the thing started while in my hand, I put it upside down while rushing to the control. When I came back, I saw my mistake, and put the device upward again.
When I was pointing to the dry oil container, I knew the oil had dripped out, but the cords themselves appeared very dry...

Anyway:

2. I thought after the diagnostic, since the motor appear to work fine and silently, that it might be a problem with the shaft might be bent, or the sleeves damaged (I am not sure what they are, because I only have the side drawing, but they look like O rings. Nevertheless, when I connected the assembly back this morning and started the motor, it did the same suttle noise which is a bit different then when the motor runs alone....after 10 to twelves seconds, when I was expecting to jamme again, the noise dissipated, and it started running smouth.

My theory or inquiry: Is it possible that the 2 top bolts holding the assembly to the motor got slightly unscrewed, while the 2 bottom one were still tight, because I did notice the top screws came out without effort at all, but a little pull was necessary to unscrew the 2 bottom one. To these bolts need to be re--tighten once or more season, something I have not done.

The assembly is newer (2018, I had to change it because it was leaking). Have not touch it since except for oiling. The motor was a refurbished unit when I purchased the pump in 2003).
If you think you know what went wrong, or if you have any suggesting of things I might have missed, please come forward.

Thank you again.

On 2021-04-17 - by (mod) - circulator pump stops and won't re-start

@Denys Picard,

That sounds as if there's a problem in the pump motor itself - a winding that opens at speed or a bad bearing;

If I've understood you correctly then take a look at ELECTRIC MOTOR DIAGNOSTIC GUIDE at https://inspectapedia.com/electric/Electric_Motor_Diagnosis.php

and let me know what you find

Watch out: testing electric motors, if you're not trained in safe VOM or DMM use, could get you shocked or killed.

On 2021-04-17 by Denys Picard

@Denys Picard, @Denys Picard, Just a note: seemed obvious to me, but in the circumstances...the zone valves operate at 24V...the Voltage at the pump is 120V, and slightly volatile (118.5 V - 120.5V), but that is in sync with the feed. Thank you.

I have a dual Electric/heating oil system which uses a Honeywell Aquastat L8148, and 2 zone valves (Schneider Electric - Two position Spring Return Valves). The whole system probably handles about 25 US Gallons. The Pump is a G&B 1/12 HP circulator pump.. It worked fine all winter

I closed it for a week, and now when I start it back, the pump will run for 10 to 15 seconds when there is a heat call and stop. I thought something might be jamming the propeller, so I took the pump out of its Pump Body.

Out of its enclosure, I tested it again, same problem, it runs 10 to 15 seconds and then stops. No noise of relays jammed, everything works, both boilers, the zone valves I can hear engage when the heat call starts prior to pump start, and when the circulator stops, you can hear them close.

I have no error messages on my secondary control, a Honeywell R7284U (Universal Digital OIl Primary). I checked the inner of the Aquastat, no visual or odor damage observable. Voltage is slightly volatile (23 to 25 Volts). That is it. What could it be?

On 2021-02-16 - by (mod) - "no heat" and "circulator won't run" diagnostic checklist

Thank you very much for taking time to write this "no heat" and "circulator won't run" diagnostic update, Ma.

We ought to remember to keep as a critical step in any no-heat diagnostic for hot water heating systems a check on whether or not the circulator pump is actually turning on in response to a call for heat. That includes checking

All the reasons that a circulator might NOT start

- thermostat or thermostat wire defect or thermostat not calling for heat

- bad end-switch on a zone valve

- lockout by the aquastat that has found boiler temperature too low (priority to a tankless coil via the LO setting)

| - a wiring defect

| - a bad circulator relay

- a failing circulator motor (gets hot, starts only when cooled-down)

- a failed circulator motor (won't start even when voltage is applied directly to the motor leads) or motor start capacitor (present on some circulator motors)

- other causes listed above.

On 2021-02-16 by ma2b16

Thanks, after further investigation, I discovered that I have 2 bad end switches on my zone valves. One did not work at all and the other was intermittent meaning it was sometimes closing the circuit and other times not. I can't find an exact replacement for the end switches yet but still searching.

In the meantime, I opened the one that wasn't working and found that it has to be pushed very deep to make contact so I placed a piece of plastic in between the plastic button and the contact to make up for the space and now it works fine. The other one seems to like it's going to eventually be the same problem so I did the same to that one as well and now both the end switches make good contact.

This is temporary until I find suitable end switch replacements. What I have come up with is part number 272744B for honeywell zone valves. Or the number stamped on the outside of my switches say V5C010UB3.
Thanks for the help.

On 2021-02-10 - by (mod) - plugged a 120VAC cord directly to the circulator to make sure it was working

It appears to me that your gap between high limit and low limit is adequate to avoid circulator lockout.

Simple test that I often try and have seen other Heating extra is to eliminate the thermostat and it's wiring from the equation by jumping the thermostat terminals at the aquastat.

If a call for heat right at those terminals in the aquastat causes it to correctly turn on the heater then we suspect the actual thermostat wires or the thermostat connections or the thermostat itself

On 2021-02-09 by ma2b16

Hi I have a Burnham Furnace with Honeywell 8124 Triple Aquastat and Taco 007 Circulator. Initially I had no heat in the radiators. I determined that the circulator pump was not running so I replaced it. After install, it still would not turn on.

So plugged a 120VAC cord directly to the circulator to make sure it was working. It was. Next I connected a Voltmeter to the Aquastat wires for the circulator and was not getting any voltage (after about an hour of monitoring the voltmeter).

Determined that my Aquastat was not sending 120VAC to circulator. Replaced Aquastat and had similar symptoms for a few cycles of the boiler. After a while, it eventually turned on the circulator pump.

Thought I had it figured out until I noticed at night (especially cold nights) that the thermostat was calling for heat but the temp would never go up. Checked the circulator and it was not running again. Not sure if it is some kind of Circulator Lockout or something else. My Hi Limit setting is about 195F, Lo Limit is about 165F and the Diff is either 20 or 25. Any help would be appreciated.

On 2020-11-22 - by (mod) -

Some water an pass a circulator even if the impeller is damaged

If the system is air bound it may be only partly-so - that is it may restrict but not totally block flow, or readiators ahead of the blockage get hot but not ones past it.

On 2020-11-18 by FER

Danjoefriedman,

Thanks very much for responding. A couple of follow up questions;

1. If the circulator is in fact not working where the impeller might be blocked/damaged, would water still be able to flow through it? I ask because when I open a faucet after tstat has activated the heat, then the hot water does flow through the air handler coils and the warm air heats the house just fine until the tstat shuts off.

2. If the system is air bound, can it somehow still operate normally after I get the hot water flowing as I indicate in #1?

The hot water itself is coming from a tankless. After the hot water leaves the tankless, the first pipe it hits is the air handler hot water intake loop. (The return loop feeds into the cold water intake of the tankless.) The next pipe (after the air handler intake) goes into the mixing valve that then feeds the domestic hot water.

On 2020-11-17 - by (mod) -

Fer

Here are a couple of things to check:

1. Just because a circulator motor is running that does not mean that the circulator is working. For example, the motor may spin but the impeller could be blocked or damaged, so no water or little water is moved. It's trivial to confirm that a circulator is actually circulating water by monitoring pipe temperature.

2. Your system could be air bound; even after bleeding some air from a hydronic system there can be more; sometimes it's hard to get air out of a horizontal run.

In the ARTICLE INDEX you'll find our articles on AIRBOUND HEATING SYSTEMS that describe how to get past that blockage.

The fact that you are seeing hot water getting to the air handler when you run hot water at a sink suggests that your domestic hot water is made by a tankless coil or by an indirect water heater.

From your description it sounds as if your system piping is circulating domestic hot water (for washing and bathing) through a building heating source (a coil in an air handler) which in my opinon is a bit odd.

I'd want the tech to map piping and controls and to sort that out for sure.

It's also possible that there's a control wiring error

I just don't have enough clear information. Eg. is it really the case that the same Taco circulator is running an indirect water heater and the heating coil in the air handler loop?

On 2020-11-17 by FER

I have a three year old First Co hydronic system that has been running without issue summer/winter since it was installed. The air handler has a Taco 006-BC7-17IFC. Yesterday the system was serviced for fall tuneup. When heat is turned on at tstat, hot water is not getting to air handler coils but HVAC tech says Taco is running because his sensor shows it pulling amps. Here's the tricky part... if hot water is turned on at any sink in the house for a few seconds after tstat turns on heat, then hot water gets to air handler coils and runs fine until tstat reaches set temp

. I do not need to keep the sink hot water running in order for hot water to reach air handler. But if I don't run sink hot water to get it going, hot water never reaches the air handler. The hot water loop to the air handler is separate from the hot water line that feeds the sinks/showers but all are off the same water tank. I also bled the air handler coil. Any ideas on what might be happening or things I should troubleshoot is greatly appreciated.

On 2020-10-21 - by (mod) -

Danny

Causes of a circulsror pump motor high load warning

Include the possibility of a failing or seizing rotor bearing or motor bearing, debris in an impeller assembly - clogging low voltage supply, pump cavitation (air in the heating system and piping, and possibly an unusually high head pressure on the system for example if you are trying to circulate to an altitude or height above what the manufacturer permits

Even a new circulator pump bearing can be damaged if the pump is not installed with correct alignment, though I've seen that problem more-often on older circulators that have a heavy and separate motor.

Uncommon: improper pump installation or mounting position.
EG:
Obstructed outlet or inlet piping: "It is recommended that the1900e series pumps be installed with at least 5 to 10 pipe diameters of straight pipe on the inlet and outlet of the pump. "
or
Improper mounting with control module "down" - that permits water to leak into the electrical components of the circulator

Less common: wiring run too long for wire size & circuit ampacity - voltage drop;

Also see the diagnostics at ELECTRIC MOTOR OVERHEATS inspectapedia.com/electric/Electric-Motor-Overheating.php

On 2020-10-21 by Danny

my taco 2 inch taco 1915e runs for a few hours then starts blinking 2 red lights meaning over current..... this is a brand new pump works fine when running.... can someone Help ??? I have the correct volts and have no aquastat connected

On 2020-10-21 by (mod) - Taco 1910e Circulator Over Current Error Code diagnosis

Danny

Causes of a circulator pump motor high load or over-current warning

Include the possibility of a failing or seizing rotor bearing or motor bearing, debris in an impeller assembly - clogging low voltage supply, pump cavitation (air in the heating system and piping, and possibly an unusually high head pressure on the system for example if you are trying to circulate to an altitude or height above what the manufacturer permits

Even a new circulator pump bearing can be damaged if the pump is not installed with correct alignment, though I've seen that problem more-often on older circulators that have a heavy and separate motor.

Uncommon: improper pump installation or mounting position.
EG:
Obstructed outlet or inlet piping: "It is recommended that the1900e series pumps be installed with at least 5 to 10 pipe diameters of straight pipe on the inlet and outlet of the pump. "
or
Improper mounting with control module "down" - that permits water to leak into the electrical components of the circulator

Less common: wiring run too long for wire size & circuit ampacity - voltage drop;

For readers needing the IO Manual for this circulator pump,

See TACO 1900E ECM HIGH EFFICIENCY CIRCULATOR MANUAL [PDF] including the Taco 1915E

Also see the diagnostics at ELECTRIC MOTOR OVERHEATS inspectapedia.com/electric/Electric-Motor-Overheating.php

On 2020-10-21 by Danny

my Taco 2 inch taco 1915e runs for a few hours then starts blinking 2 red lights meaning over current..... this is a brand new pump works fine when running.... can someone Help ?

I have the correct volts and have no aquastat connected

On 2020-04-28 - by (mod) -

Dhiresh

Sure.

Check the circulator relay - it should be turning on the pump;

Check the thermostat terminals at the circulator relay - jumping those should turn on the pump.

Check for shorted or disconnected thermostat wires.

Watch out: the pump may be running fine and the problem could be an air-bound heating zone.

Please see diagnostic details at CIRCULATOR OPERATION CHECKS

On 2020-04-28 by Dhiresh

Hello I have a Bell Gosset Circulator for my gas fired boiler. A couple of my rooms were not heating so I decided to check out and see if the pump was working. I connected it directly to a power outlet and the pump is working. The issue I think is that the boiler is not activating the pump so it may be an electrical issue. Can anyone advise a fix ?

On 2019-11-16 by (mod)

Easy to check: the transformer will have an output of 24VAC. - using a DMM or VOM one can check that right at the transformer;

Take care not to touch live voltage - you can be shocked or worse.

On 2019-11-16 by Dan

I've replaced the taco pump, both relay switches and thermostat on my hydronic heating system. It's ran off the water heater and water heater is working proper. Could it be the transformer that has gone bad?

On 2019-09-03 by (mod) - gas boiler circulator wont' turn on after power outage

It should be easy to diagnose this problem by bypassing the aquastat's circulator relay - by jumping the circulator proper terminals.

Watch out: if you're not familiar with proper and safe electrical testing: you could damage a control or make the equipment unsafe or get shocked or worse.

Manuals for your boiler are

at ALLIED ENGINEERING BOILERS & WATER HEATERS (EZ-RECT)

On 2019-09-03 by Dean

I have a super hot mini gas boiler after a power outage the furnace wont work properly the unit turns on no circulation.

Diag the pump fried replaced with new still doesnt cycle. Burner turms on zones open everythong but pump. Bad aquastat?

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?

Reply:

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.


...

Continue reading at CIRCULATOR OPERATION CHECKS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see CIRCULATOR PUMP WON'T START FAQs - questions and answers about dead circulator pumps posted originally on this page.

Or see these

Recommended Articles

Suggested citation for this web page

CIRCULATOR PUMP WON'T START at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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