# Boiler still runs even when thermostat is off



## jamegail1 (Sep 15, 2010)

:help:I have a two zone Smith GB100W gas boiler that still runs after the thermostat has reached the desired temp. Even when you shut off the heat at the programmable thermostat the boiler keeps running. I replaced the thermostat to no avail. I am wondering whether it is the Honeywell aquastat controller.I have model L4080b on the boiler. Any help would be appreciated. Thanks again , jamegail1


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## beenthere (Oct 11, 2008)

Is the second zone, an indirect water heater?


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

The second zone is not for a water heater. It is for the second floor of my house.


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## beenthere (Oct 11, 2008)

Are you sure that thermostat isn't calling of heat?

Is there only one aquastat on the boiler?


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## jamegail1 (Sep 15, 2010)

*Boiler still runs when thermostat is off*

Thanks for replying to my post beenthere.There is only one aquastat controller on the boiler. Both thermostats are turned to the off position. The boiler turns on even when it is shut off at the thermostats.


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## AllanJ (Nov 24, 2007)

The boiler itself may have an internal control to keep itself at a certain minimum temperature so when the thermostats call for heat, the rooms will get heat faster.

In a typical system the aquastat controls the burner independently of the thermostats and circulator pumps controlled by the thermostats send the heated water to each zone.

If there is a domestic hot water coil then the aquastat will maintain the boiler temperature for the hot water and the act of doing so will keep the boiler ready to supply heat for the rooms.


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## beenthere (Oct 11, 2008)

I don't recall Smith having a gas boiler with a tankless coil.

Its probably the R8225D relay stuck closed.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

Thanks for posting. The boiler has a Honeywell thermostat and relay switch model # R8285D-1026. I don't know if this will help or not. Both thermostats are turned off. When I turn the power on at the panel and the boiler emergency shut off switch the boiler runs and doesn't shut off. This just happened all of a sudden. Any help would be appreciated.


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## beenthere (Oct 11, 2008)

Sounds like the relay is stuck closed.

Needs replaced. Just the relay though.


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## jamegail1 (Sep 15, 2010)

*Boiler still runs when thermostat is off*

Thanks beenthere !!! I will try that first and hope that it works. What part of Pa. are you located in ? My Dad lives out by Johnstown. Just curious. Again thanks. I will post after I install the relay.:thumbup:


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## beenthere (Oct 11, 2008)

Lancaster county.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

I just received the new R8285 control center yesterday. I went and tried to replace only the relay switch and that didn't work. I then installed the transformer part of the control center and that failed also. Any other suggestion out there ? Thanks in advance, jamegail1


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## beenthere (Oct 11, 2008)

Do you have a multimeter, and know how to use it.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

Yes I have a multimeter.


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## beenthere (Oct 11, 2008)

With thermostat turned off, or set to lowest temp setting.

See if you are getting 24 volts between the W and C terminal on the relay.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

Update to my post is as is : Today I installed a new aquastat L4080B-1253 and the problem persists The only difference is that when the boiler got to the low setting of the aquastat it shut down. Someone said that it might be the gas valve. I don't know if thats possible because we are getting gas. Any suggestions are appreciated.


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## TimPa (Aug 15, 2010)

still something in the aquastat contacts i think. sounds like it's wired to the n.c. contacts now. did you pull parts off the new aquastat? double check your wiring.


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## beenthere (Oct 11, 2008)

If it was wired to the NC contacts. Then it wouldn't shut off unless the stat was calling for heat.



Have you checked to see if the stats are calling for heat intermittently when they shouldn't be.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

How do I check to see if that's the problem? The thermostat is still not turned and the boiler is still running. It shut down when it reached the lowest setting on the aquastat. Is it possible that there is a short in the wiring coming from either one of the thermostats ? What size wire do I use if I change out the wiring? 18 gauge? Thanks again.


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## beenthere (Oct 11, 2008)

Use your meter. And see if you have 24 volts from G to C on the relay center.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

I have a simple question. Do I do this with the power off to the boiler?


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## beenthere (Oct 11, 2008)

No. The power needs to be on, to see if it has voltage across the G and C terminals.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

It was reading 16.8 v. I hope I did it right. I put the neg on the g and the pos on the c.When I did this I had turned on the boiler and both thermostats.When it reached 220 degrees the boiler shut down. I then shut down the lower floor thermostat.I bought 18v wire for the thermostats and will change that first thing tomorrow. I then went to turn on the heat again and just turned on the breakers. This time the boiler didn't start. I then turned on the thermostat downstairs and the boiler started and then shut off when it reached its high temp on the aquastat. I can't figure it out !!!


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## beenthere (Oct 11, 2008)

The test is best done with the thermostats turned off, or down. So you can see if a wire is shorting and making a false call for heat.


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## jamegail1 (Sep 15, 2010)

*boiler still runs even when thermostat is off*

Well I have an update. The voltage was 31 with the thermostats turned off. It seems as if the Aquastat was the culprit. I ran new wire from the downstairs thermostat to the boiler and everything seems to be working fine.It turns on and off when called for by the thermostat.It has stopped running when the thermostat is turned off also. Thanks for all that replied. I have learned a lot about my boiler now. Special shout out to beenthere for you help.


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## beenthere (Oct 11, 2008)

The thermostat wire had a short in it. Its a somewhat common occurrence.

Glad to hear you got it fixed.


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