gas furnance won't automatically stop heating at correct temperture


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Old 03-20-13, 07:05 AM
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gas furnance won't automatically stop heating at correct temperture

Our furnace will not stop running. We just put a new Honeywell wi-fi programmable therostat on. It is not the thermastat because this problem has continued with 3 different ones.

We have been turning the circuit breaker off in order to get the furnace off.

What needs to be done to get the furnance to stop running at the temperature we have it set at? Thank you, Lynne
 
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Old 03-20-13, 09:12 AM
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First, we need the make and model of the furnace and the model of the thermostat would also help.
Does the furnace continue to heat past the set temperature or does the blower just keep running?
 
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Old 03-20-13, 10:33 AM
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"It is not the thermastat because this problem has continued with 3 different ones. "
Is that three different ones of the same model thermostat ? Usually included with the t-stat is a phone number to call and they will walk you through the install.
 
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Old 03-20-13, 10:49 AM
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Does the burner continuously stay lit or its just the blower that keeps running. Sounds like a stat wiring issue. Dd you have this problem before you installed the original wi-fi stat?
 
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Old 03-20-13, 01:26 PM
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Possibilities:

1. The t-stat is miswired
2. There's a short in the t-stat wiring.
3. The control board is bad

Shut off the power, open up the furnace and disconnect the low voltage wire connected to W. (tape it off so nothing shorts out)

Restore power and see if it heats with nothing connected; if it does, you have a bad board. I don't recommend replacing it yourself.

If it doesn't, make sure the wire colours at the t-stat match the colours at the board. (Red going to R on both sides, White going to W on both sides. Actual colours don't matter)

If the wiring looks okay, check the resistance between R and W at the furnace control board with everything off. (t-stat switched to off, power to furnace off)

If the resistance isn't infinity, there's a short in the t-stat wiring.
 
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Old 03-22-13, 08:55 AM
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more info. to go with the question

Hi, thank you everyone. I asked the question & here is some more info.
the furnace is a Air Temp, model number is 4212-30 serial ol835952

We called the number in the book that came with the t-stat & they told us to get an electrician. My son's friend has a journeyman's license & he looked at it & wasn't able to help.
 
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Old 03-22-13, 08:59 AM
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The burner continuously stays lit....No we did not have this problem before we installed the original wi-fi stat. When we put the old mercury t-stat back on this problem is the same way so we think it has nothing to do with the t-stats.
 
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Old 03-22-13, 04:19 PM
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Follow the instructions I posted if you have a multi-meter and know how to use it.

Otherwise, call an hvac tech, not an electrician.
 
 

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