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Old 09-16-2010, 01:22 PM   #1
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furnace always on


My furnace wants to always be on. I tried the basics like making sure the thermostat is set right making sure it's set of off and I even turned the AC on and the furnace still runs. Even when the blower is off the burners are going. I've replaced the thermostat to no avail. I'm out of ideas since I'm not very knowledgeable about this realm of home repair. Any ideas of what to look for before I call in an expert?

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Old 09-16-2010, 01:25 PM   #2
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furnace always on


disconnect the red or white wire from the t.stat & see if it still runs

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Last edited by kenmac; 09-16-2010 at 01:28 PM.
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Old 09-16-2010, 02:34 PM   #3
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furnace always on


The high temperature cutoff may be malfunctioning.

Does the burner shut off sooner or later? If not, you are wasting tremendous amounts of fuel.

On some furnaces the blower and burner may both cycle on and off not always at the same time.
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Old 09-16-2010, 02:38 PM   #4
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furnace always on


I'll disconnect the white and red wires when I get home. If that works what is the problem and how can I fix it?

As far as I know it does not shut off. I came home one day to a 90 deg house with the AC running and the furnace fighting against it. After trying a few simple things to try to get the furnace to shut off I ended up turning off the gas. If I cut power to the furnace and turn it back on after a few minuets the furnace wants to kick on again. I'm not sure how long it would run if I just let it go.
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Old 09-16-2010, 02:50 PM   #5
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furnace always on


Flipping off the circuit breaker should shut down the furnace.

An ordinary furnace serviceman who handles that brand should be able to fix it. Also, many furnaces nowadays have electronic circuitry and the circuit board may be the defective item.

The "service manual" for your furnace model may be in the Internet. You would have to be familiar with such steps and language as "Measure voltage between point T and point AA" and "If voltage is between X and Y then go to step 5.5"
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Old 09-16-2010, 05:32 PM   #6
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furnace always on


Disconnect W And R at stat. if it still runs, Disconnect R and W at furnace. If it still runs, control at furnace is bad.
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Old 09-17-2010, 09:04 AM   #7
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furnace always on


Disconnected the red and white at the stat and it still ran, disconnected the red/white and furnace and it turned off. Does this mean I have a bad thermostat or possibly the wrong kind?
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Old 09-17-2010, 03:02 PM   #8
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furnace always on


It means the wires from your furnace to your thermostat are shorted out somewhere. You'll have to run new wires.
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Old 09-17-2010, 03:16 PM   #9
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furnace always on


good thing I have good access to them. Looks like I know what I'll be doing this weekend.

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