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Fix a circulator pump that will not run

We'll confirm the thermostat and zone valve, check power and the aquastat, test the pump, and free or replace it if faulty—or tell you when to call a pro.

Troubleshooting · Home maintenance
15–60 min
What you'll need
  • Multimeter (for testing voltage)
  • Screwdriver set
  • Replacement circulator pump (if pump has failed)
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Steps

Goal: Confirm the thermostat and zone valve, check power and the aquastat, then isolate the pump fault.

  • Set the thermostat to heat and confirm at least one zone valve is open.
  • Good: The thermostat is calling and a zone valve is open. Proceed to Check power and control.
  • Bad: The thermostat is not calling or no zone valve is open—fix that first.

Check power and control

Goal: Rule out power loss and control failure before testing the pump.

  • Confirm the circuit breaker for the boiler has not tripped. Check the boiler or pump switch.
  • The pump is controlled by an aquastat or zone valve end switch. Confirm the boiler has reached temperature and the control is sending the signal.
  • Good: Power is on and the control is sending the run signal. Proceed to Test the pump.
  • Bad: No power or control not sending signal—fix those first.

Test the pump

Goal: Confirm whether the pump is energized and responding.

  • Locate the circulator pump on the boiler or pipe.
  • With the thermostat calling, listen at the pump. Feel the pipes for water flow.
  • Good: The pump runs and the pipes warm—pump is working. Bad: The pump hums but does not spin—seized. Bad: No sound—no power to pump.

Free or replace pump

Goal: Free a seized pump or replace a failed pump.

  • If the pump hums but does not spin: shut off power, turn the shaft with a screwdriver, restore power and test. If it runs, it may seize again—plan to replace.
  • If the pump receives power but does not run, or is leaking: replace the pump. Shut off the boiler, drain the system, disconnect the pump, install a replacement, refill and bleed. Call a pro if you are not comfortable with plumbing.

When to get help

Call an HVAC technician if:

  • The pump hums but does not spin after freeing.
  • The pump is leaking.
  • You have replaced the pump and it still does not run.
  • You are not comfortable with electrical or plumbing work.

If you smell gas near the boiler, evacuate and call 911 or your gas utility from outside.

Verification

  • The circulator pump runs when the thermostat calls for heat and a zone valve is open.
  • Hot water flows through the zones—radiators or baseboard heat up.
  • No humming without flow (seized) and no leaks at the pump.
  • The pump responds when the control sends the run signal.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm thermostat and zone valve Verify the thermostat is calling and at least one zone valve is open.
  2. Power and switch Check circuit breaker and boiler or pump switch.
  3. Aquastat or control Confirm the aquastat or zone valve end switch is sending the run signal.
  4. Free or replace pump Try freeing a seized pump; if it fails, replace the pump.
  5. Call a pro Pump still does not run, pump is leaking, or not comfortable—call an HVAC technician.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Boiler type and pump model
  • Whether the pump hums when the thermostat calls
  • Voltage at pump terminals (if tested)
  • Steps already tried

Is the thermostat calling and a zone valve open?

The pump runs when the boiler calls for heat and at least one zone valve is open.

Set the thermostat to heat. Confirm at least one zone valve is open. Good: thermostat calling and zone valve open. Bad: thermostat not calling or no zone valve open—fix that first.

Yes No

You can change your answer later.

Fix thermostat or zone valve first

If the thermostat is not calling, see Fix a thermostat that will not respond. If the zone valve does not open, see Fix a zone valve that will not open.

Done

Is power on and the breaker not tripped?

Check the circuit breaker and boiler or pump switch.

Check the circuit breaker for the boiler. Check the boiler or pump switch. Good: breaker on and switch on. Bad: breaker tripped or switch off—reset and test.

Yes No

You can change your answer later.

Does the pump hum when the thermostat calls?

A hum with no water movement often means a seized pump. No sound means no power to the pump.

Listen at the circulator pump when the thermostat calls. Hum but no flow: pump seized—try freeing the shaft. No hum: no power—check aquastat or zone valve end switch. Runs normally: pump is working—look elsewhere.

Yes (hum but no spin) No

You can change your answer later.

Free the pump shaft

Shut off power. Turn the pump shaft with a screwdriver. Restore power and test. If the pump runs, it may seize again—plan to replace. If it still does not run, replace the pump or call a pro.

Done

Check aquastat and wiring

Confirm the aquastat is set correctly and the boiler has reached temperature. Check the zone valve end switch and wiring. Test for voltage at the pump terminals. If no voltage, the control has failed. If voltage present but pump does not run, the pump has failed.

Done

Call a pro

Call an HVAC technician if the pump still does not run after checks, the pump is leaking, or you are not comfortable with electrical or plumbing work.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would a circulator pump not run?
Common causes: no power, a tripped breaker, the aquastat or zone valve end switch not closing, or a seized pump. The pump runs when the boiler calls for heat and a zone valve is open—check the control circuit first.
Can I fix a circulator pump that will not run myself?
Yes, you can check power, the breaker, and the aquastat. You can try freeing a seized pump by turning the shaft. Replacing the pump requires draining the system and plumbing—call a pro if you are not comfortable.
When should I call an HVAC technician for a circulator pump?
Call a pro if the pump hums but does not spin after trying to free it, the pump is leaking, you have replaced the pump and it still does not run, or you are not comfortable with electrical or plumbing work.

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