Circulator pump leak at mounting flange (C) Daniel FriedmanCirculating Pump Bypass
How to bypass a heating zone circulator pump that is not working - emergency heat

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Heating zone circulator pump bypass: how to circulate hot water in a hydronic heating system if the circulator or zone valve is not operable: bypassing the heating circulator pump or latching the zone valve open can get heat into the building even if the circulator pump itself is not working - maybe.

Our page top photo shows that a heating circulator pump motor has been removed completely while waiting for replacement. How can we get heat to flow in this building?

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

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Bypass the Circulator: Question: OK to run the boiler if the circulator is not working right?

Zone Valve manual control lever (C) Daniel Friedman(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.
Thank you


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

Boiler check valve or flow control valve (C) Daniel FriedmanIn 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.

In my photo at above left, push the metal lever all the way to the left then down to latch it in the "OPEN" Position.

See ZONE VALVES, HEATING for more details about diagnosing & fixing or replacing a bad zone valve.

The heating boiler flow control valves (photo at left) designed to prevent hot water circulating by convection when the circulator is not operating can also be manually placed in an OPEN Position.


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.

Watch out: in many but not all hot water heating systems that use a circulator pump, flow-control or flow-check valves and zone valves, you can get hot water to circulate by natural convection using the steps above. The thermostat calls for heat and provided that the boiler temperature is below the CUT IN setting on the boiler primaruy control or aquastat the boiler will cut-on, heating its water. Heated water will then rise in the heating distribution piping above the boiler and into the building.

  • Heat delivered by these methods will arrive more slowly than if a working circulator pump were in operation
  • It may be necessary to manually open the flow-control valve or check valve (shown above) in for hot water to flow.
  • If a zone valve lacks a manual open feature OR if the zone valve head has jammed and won't operate then a heating system with zone valves won't circulate heat through that zone.


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

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

Suggested citation for this web page

BYPASS a BAD CIRCULATOR at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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