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.

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

Photo above: with the zone valve latch moving freelh as shown, the zone control should open and close the valve in a reponse to a call for heat. If you pull the lever to the left and latch it "down" the zone will remain open continuously.

Hot water will circulate through that heating zone by gravity (convection) even if the circulator pump is off.

Our reader asked:

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 Kelly

Reply:

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

In 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.

See CHECK VALVES, HEATING SYSTEM for details.

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.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Is it possible to turn off one of my heating zone circulators?

I have 4 heat circulator pumps. I want to turn one off because it interferes with the radiant heat system. Is it possible to turn off a honeywell circulator pump? On 2018-10-26 by Robert

Reply by (mod) -

Sure, Robert,

Each individual circulator pump in a hydronic heating system will be controlled by an individual relay and thermostat for that heating Zone that the circulator serves.

You should be able to Simply turn the zone or room thermostat temperature setting all the way down in that zone associated with the circulator that you want to turn off.

Thanks for asking.

Can the boiler supply heat to radiators if the circulator is not running?

I have a Peerless model # MMR-85-WC boiler. I have heat at my downstairs radiators, however i dont think circulator pump is operating becaused i dont have heat to upstairs radiators.

Can the boiler supply heat to radiators even though i dont hear circulator pump. I normally dont have gate valve open for upstairs heat, gets too hot at night. On 2018-01-03 by Frank

Explkanation and diagnostic suggestions by (mod) -

Frank

Yes, hot water can circulate through some parts of a hot water heating system and not others, by convection (or "gravity") even if a circulator pump is not running.

And hot water flow can be blocked in some portions of a heating zone even if all valves are open - as we explain at AIR-BOUND HEATING SYSTEMS.

And some circulators, such as some Taco models, are so quiet that you won't hear the circulator pump even if it's running.

If you don't have heat upstairs and you are closing a valve in the zone piping that alone would explain the trouble, right?

You can use some simple observations we explain at CIRCULATOR OPERATION CHECKS  to figure out if the circulator is running or not.

Try opening that "gate valve" that you say is closed.

How can I keep heating zone water circulating even if my heating boiler isn't working?

If my furnace stops working is there a way to put power to the circulator pump so that my pipes don't freeze. I would open a zone valve and do what? On 2015-10-16 by Jim

Answer by (mod) -

Jim,

If the furnace (I'd call yours a heating boiler) has electrical power but is not running, simply leaving it turned ON and having the thermostat call for heat will turn on the circulator pump; that should be all you need to do.

In some cases, such as most Canadian hot water heating systems, the electrical controls are connected such that the circulator pumps run continuously and the thermostat simply turns the heating boiler on and off in response to a call for heat.

I think that's done both to asssure the most-even heat distribution and to help avoid frozen heating pipes.

You can confirm this by following the electrical wiring from your circulator pumps backwards to confirm that no electrical switches are off.

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

Or see these

Recommended Articles

• CIRCULATOR PUMPS & RELAYS - home
  • BELL & GOSSETT B&G EQUIPMENT MANUALS & CONTACT
  • CIRCULATOR PUMP BASICS
  • CIRCULATOR PUMP MANUALS
  • WHAT GOES WRONG WITH HEATING CIRCULATORS?
• CIRCULATOR PUMPS vs ZONE VALVES
• ZONE VALVES, HEATING  - home

Suggested citation for this web page

BYPASS a BAD CIRCULATOR 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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