Circulator pump leak at mounting flange (C) Daniel FriedmanCirculating Pump Runs Intermittently
Diagnose & fix circulator pumps that run only at intermittent intervals
     


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Intermittent on-off heating zone operation:

Heating zone circulator pump seems to run just intermittently - it starts and stops. What's wrong, how do I fix it? We start addressing this question by asking whether or not anything is wrong in the first place.

When should the heating zone circulator be running? Then if it seems to be acting oddly, why & how do we fix it?

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

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Question: circulator pump runs intermittently

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
the boiler. my problem is the pump only comes on for about 30 seconds and thats it and it does nothing for the rads the pipe that the stat is on goes cold so i reckon the stat is on the wrong pipe,
please help. cheers

Phil said:

My circulator pump turns on then shuts off in 3-4 sec. could this be a switch?

Reply:

First I would check all of the electrical connections involved since a loose connector or a corroded connector such as a spade connector on a heater control can cause intermittent operation.

... the furnace draft fan began to pulse several times upon starting. After making sure the control module showed a steady green, ... I wiggled all the spade connectors to be sure there was good contact between the copper and aluminum. ... there only needs to be a little corrosion to cause problems. That seems to have done the trick. - M.F. 12/24/2014

Next 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.

See CIRCULATOR PUMP RELAYS & OTHER CONTROLS

and see THERMOSTATS, HEATING / COOLING for details.

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.

Watch out: other readers note: other reasons that a heating zone circulator may not run continuously include

  • Normal operation: in some areas circulator pumps are wired to run continuously if the boiler has electrical power but in others the circulator only runs in response to a call for heat. In the latter case the boiler temperature turns the burner on and off.
  • Improperly-set primary control - check your aquastat settings to be sure they are correct - see AQUASTAT HI LO DIFF SETTINGS
  • Shorting thermostat wires: a room thermostat whose wires are shorted or intermittently shorting together may turn the circulator on and off
  • Poor thermostat settings: on some systems an improperly set heat anticipator may cause the circulator to stutter on and off; this problem may also show up as "contact bounce" in the thermostat
  • Damaged circulator pump relay: in the primary control or in additional circulator pump control relays a failing switching relay can casuse funny circulator pump on-off operation.
  • Tankless coil snafu: if your heating boiler does not make use of a tankless coil to produce domestic hot water but the aquastat was installed with its factory settings that control may make the heating boiler run for no apparent reason - though usually only briefly. Some may confuse boiler-burner-on with circulator-on operation. If the thermostat is not calling for heat the circulator won't run (unless it's wired for "always on" operation).

 

Continue reading at CIRCULATOR OPERATION CHECKS or select a topic from the More Reading links shown below.

Or see CIRCULATOR DIAGNOSTICS

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

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CIRCULATOR PUMP RUNS INTERMITTENTLY at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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