FAQs about hot water heating system circulator pump control relay troubleshooting & repair.

In this article series we list & describe both circulator pump relay controls and other heating system controls that manage or impact heating boiler circulator pump operation.

Page top photo: Taco's SR503 switching relay that can control 1 to 3 circulator pumps.

Circulator Pump Relay Installation & Repair Q&A

These questions & answers about circulator relay controls or switches (used to turn hydronic heating system circulators on or off) were posted originally

at CIRCULATOR PUMP RELAYS & OTHER CONTROLS - be sure to see the advice and circulator controls discussed there.

See our index to questions & answers about installing or repairing heating zone circulators at

CIRCULATOR PUMP REPAIR FAQs - index

Photo above-left: a primary or single circulator pump relay switch is found inside of many aquastats such as this Honeywell / Resideo L8182D Aquastat.

My boiler kicks on but one circulator pump does not run

I have a 2 zone heating system with 2 circulating pumps when the top floor is turned up the furnace kicks on and heats the top floor.

When the first floor is turned on you hear a click noise from the t-stat and nothing happens went down stairs to boiler the circulation pump for the top floor is working and the pump for the first floor doesn't turn on. replaced the pump still not working.

Removed panel for the aquastat removed the 2 wires for t-stat.

I put a jumper wire on the 2 t-stat terminals.

The primary control relay clicks but the circulator pump still doesn't turn on.

Is it a bad aquastat? (Mar 30, 2015) rusty

Reply: check the circulator relay

If the circulator relay is not pulling in it's a bad relay or control.

If the relay pulls in and voltage is being delivered to the pump but the pump does not run it's most likely either an open wire or a bad pump.

Rusty said:

I wired the pump to a cord that plugs into the wall and the pump turns on.

Reply:

So we know the pump is good.

Check the wiring for continuity and check all connections.

Check whether or not the circulator relay pulls in and when it does if voltage is given to the pump.

Watch out: there are electrocution hazards in what you already did and in what you might do

Rusty said:

All the connections look fine. when I used the jumper wire the relay moved in and when removed the wire the relay pulled back

Moderator reply:

Sounds like a bad circulator relay.

 

What to do if the circuit breaker to the boiler circulating pump was tripped

When I turned the 2 thermostats up to start heating the outbuilding this fall, without response, I found the circuit breaker to the boiler circulating pump was tripped, and continued to trip immediately after each time I reset it.

The system is about 16 years old-2 zone, has a Honeywell R8285a-1048 relay and a Grundfos type UP 15-42f circulating pump. Where would be the best place to start troubleshooting this problem? On 2017-12-14 by Jerry

by (mod) -

I would go to the boiler and disconnect power to the primary control. And turn the breaker back on.

If it Trips Again then since you've disconnected everything that your heating system you would expect the problem to be in the circuit wiring itself.

No heat, just 5 PSI in the boiler - is that a bad circulator relay?

Peerless boiler firing hot water at showers...baseboards cold not heat..no air in lines...taco circulator pump only 5 lbs pressure on gauge at furnace....is there a relay to check if it's working On 2016-12-18 by Michael

by (mod) -

Michael:

5 psi is abnormally low - if the gauge is accurate there's probably a leak and also a defective water feeder valve. At low pressure the circulator may not be able to push hot water up to baseboards at higher levels.

Circulator Relay Switch on the R8845U won't start one of my heating zone circulators

Switch relay r8845u won't start 1of 2 circulator pumps On 2015-11-27 by Tim

by (mod) -

Tim, usually each pump has its own start relay. One of these relays, or its controlling thermostat mat be bad.

Two Stage Boiler in Condo needs relays and clock replacement for each boiler stage - what's that clock about?

Hi - we have a two-stage boiler in our 4-unit mountain condo unit that provides hot water for consumption as well as for sidewalk ice melt (heated glycerine lines).

The unit is about 8 years old, and we're being told by the company that services it we need to replace two relays and a "clock" for each boiler stage.

Is 8 years a reasonable lifespan for relays? And do you have any idea about what is the "clock" that needs replacing? Thanks! On 2014-05-31 by JeffHOA

by (mod) -

Jeff,

Sorry I don't know what the tech is referring to either.

Relays that control the switching of equipment might need replacement if the relay was burned or damaged, and such damage could occur in the time you cite.

I don't know what clock they're talking about. Perhaps you could ask that someone point out the part to you - note its brand and model number and let us know.

I suspect that a clock / timer is being used to run the boiler to de-ice sidewalks during certain times of the day or it's providing more detailed controls over boiler internal operation cycles.

Daniel

by JeffHOA

Thanks, Daniel - will check on the clock and let you know. Appreciate the validation on the relays.

...

Daniel, I heard from our maintenance manager who is coordinating the boiler repair.

He says: "The clock is to time and signal cycles (eg, pre purge, attempt to light, post purge, etc. ).

The boiler company recommended the clock be changed out along with the failed relay."

Sounds like it's not that expensive, but funny that something like an electronic clock would need to be replaced. Thanks for your help.

by (mod) -

Jeff

Thanks for the clarification. Your view is reasonable.

I think tech figure it's easier and safer to swap out multiple old parts (even if some may be ok) than to have to return to the job. Considering service call costs it may be a less expense approach overall

 

When does the circulator pump start? at what temperature

I have a hot water burner with a circulating pump when does the pump start? does it start at a certain temp.?
would you see the shaft spinning when it starts? it is a taco 110 pump. (Oct 27, 2015) John said:

Reply:

John, on most heating boilers in the U.S. the thermostat turns on the circulator pump while independently, the temperature of the boiler, controlled by the aquastat, turns the burner on or off.

When room temperature falls below the set temperature on the thermostat then the circulator pump will start.

In Canada at many hydronic heating system installations the circulator runs continuously and the thermostat will turn the boiler on when room temperatures fall below the set temperature on the thermostat.

See AQUASTAT CONTROLS - home

and

See CIRCULATOR PUMP RELAYS & OTHER CONTROLS

and

See THERMOSTATS, HEATING / COOLING - home

Why does the heating zone circulator keep running after the boiler turns off?

Is the circulate pump still running for 2-3 munites after the boiler shuttoff normal ?

Also the circultor pump starts running for 30 seconds before the boiler turns on On 2014-02-19 by gary

by (mod) -

Gary that sounds correct. When heat is running the boiler will shut off when its internal temperature reaches the HI limit.
The circulator will continue to run until the call for heat is satisfied at the room thermostat.

When heat is not already running, when the room thermostat calls for heat the thermostat turns on the circulator to send hot water to the heating zone baseboards or radiators; as returning cool water drops boiler temperature the boiler's burner will then turn on.

Heating zone circulator only works if I turn power off and back on

Circulating pump stop working but when I turn off and back to on the furnace then it starts working. On 2014-02-11 by circulating pump

by (mod) -

Circ:

It sounds as if there may be a problem with the circulator relay or even the pump itself;

...

...

Continue reading at CIRCULATOR PUMP RELAYS & OTHER CONTROLS - topic home, or select a topic from closely-related articles below, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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• CIRCULATOR PUMPS vs ZONE VALVES

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