Furnaces will not shut off

Old 04-23-09, 03:18 PM
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Join Date: Apr 2009
Location: Oklahoma
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Furnaces will not shut off

The temp here in Oklahoma is about 80 degrees, yesterday the upstairs furnace came on. I check it out and the thermo. is turned "off" but the furnace continues to run, until I flipped the breaker. I called the repair man (that repaired it in Dec.) and told him what was going on. He told me even if the thermo. is turned off the furnace will still come on because it goes off of attic temp. He also tells me to go into the attic and unplug the furnace and put out the pilot. I'm feeling like this guy is just not wanting to back up his work??? Please help with this question.
Old 04-23-09, 03:48 PM
Join Date: Dec 2004
Location: San Jose,Ca
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I suspect the gas is not on in the furnace. The blower is probably running due to the excessive heat in the attic. Most older furnaces utilize a "fan control" that is thermally activated. It is set for a desired "on" temp and when the heat exchanger reaches that temp during normal operation the fan comes on. When the thermostat setting is satisfied the burners go off and in a little while the blower has cleared the heat from the heat exchanger and the blower goes of at the predetermined "off" temp. Well the attic is so hot it has caused the fan control to think the burner is on and started the blower. Newer and some older furnaces usea "fan timer board" which is not thermally activated. If you do not have air conditioning then I would do as your repairman suggests. However be sure to verify the gas to the burners is not on. If you happen to have a stuck gas valve, unplugging the furnace could lead to a fire without the blower running. If you do have a/c turn it on to cool down the fan control.

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