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

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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.

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

Reader 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


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.


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.

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:


How To Tell If A Heating Boiler Circulator Pump Is Working

  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.


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.


Continue reading at CIRCULATOR OPERATION CHECKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


If you are not getting any heat at all out of a cold baseboard or radiator, see COLD HOT WATER BASEBOARD / RADIATOR

Or see these

Hot Water (Hydronic) Heating Boiler Circulator Articles

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