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Old 09-15-2010, 01:21 PM   #1
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Boiler still runs even when thermostat is off


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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Old 09-15-2010, 06:21 PM   #2
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Boiler still runs even when thermostat is off


Is the second zone, an indirect water heater?

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Old 09-15-2010, 08:27 PM   #3
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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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Old 09-15-2010, 08:40 PM   #4
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Boiler still runs even when thermostat is off


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

Is there only one aquastat on the boiler?
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Old 09-16-2010, 08:28 AM   #5
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Boiler still runs even 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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Old 09-16-2010, 02:26 PM   #6
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Boiler still runs even when thermostat is off


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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Old 09-16-2010, 05:56 PM   #7
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Boiler still runs even when thermostat is off


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

Its probably the R8225D relay stuck closed.
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Old 09-16-2010, 08:34 PM   #8
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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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Old 09-16-2010, 08:51 PM   #9
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Boiler still runs even when thermostat is off


Sounds like the relay is stuck closed.

Needs replaced. Just the relay though.
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Old 09-16-2010, 09:24 PM   #10
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Boiler still runs even 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.
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Old 09-16-2010, 09:28 PM   #11
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Boiler still runs even when thermostat is off


Lancaster county.
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Old 09-22-2010, 12:14 PM   #12
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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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Old 09-22-2010, 05:44 PM   #13
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Boiler still runs even when thermostat is off


Do you have a multimeter, and know how to use it.
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Old 09-22-2010, 07:40 PM   #14
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Boiler still runs even when thermostat is off


Yes I have a multimeter.
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Old 09-22-2010, 07:43 PM   #15
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Boiler still runs even when thermostat is off


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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