Tstat is not responding


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Old 02-28-12, 01:05 PM
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Question Tstat is not responding

I have an old gas furnace (Duo-Therm) inside my apt. It has a millivolt gas valve with 4 electrical contacts and they are labeled Gen, Aux, and Thermo (I know only 3 labels). It has a Hi Limit thermostat in series with the wall Tstat. I can turn the pilot on and if I turn the dial on the gas valve to "On" the burners ignite and after few minutes the blower comes on and works fine. But when I try to turn the heat off using the wall tstat it is not responding even though I replaced Tstat with a new one for millivolt gas valves so I turned the furnace off using the dial. I get reading of about 385 millivolts at the thermopile contacts. Do I need to replace the gas valve, which is ITT General Control or the thermopile, which I sanded the white powdery residue off of it? By the way there is no transformer
Connected to it. Checked the safety switches both of them are ok.
 
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Old 02-28-12, 03:11 PM
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Try disconnecting one of the wires to the thermostat at the gas valve. If the burners still stay lit the valve is probably sticking open. You can try tapping on the gas valve with the handle of a table knife to see if that frees it.

Don't pound on the gas valve though ---mild tapping to see if it will free itself is worth a try.
 
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Old 03-03-12, 11:11 PM
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thanx SP I tried it and the burners did not go out. Could it be the thermopile ? Because I don't get more than 416 mv.
 
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Old 03-04-12, 08:57 AM
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You have a stuck valve. Call a competent repairman to replace it, it's not a suitable DIY job.
 
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Old 03-05-12, 12:43 PM
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Thanx SeattlePioneer for your inputs. I will have it replaced and let you know the outcome.
 
 

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