Furnace won't stay OFF!

General topics about all things heating, ventilation, air conditioning and refrigeration.

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Furnace won't stay OFF!

Post by sherrilhopper » Mon Nov 29, 2010 8:44 pm

My furnace suddenly has a mind of its own. When the thermostat is turned off, or if the tempurature on the thermostat is set below the current (or expected) temperature, the furnace frequently turns on and blows cool air. The only thing to do at that point is turn off the power to the furnace.

Does anyone have any thoughts about what is going on and what I should do or check?

Thank you!

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- Furnace won't stay OFF!

Post by Hyack » Tue Nov 30, 2010 11:47 pm

Newer home? Could be a simple answer. Some homeowners are unaware that there may be a ventilation switch near the thermostat that controls the blower fan. It would look like a light switch but not seem to control anything that lights. Check to see if that switch is off.

Also, along those lines the interlock relay (controlling the furnace fan when you run your fan over your range/oven) could be wired incorrectly. Open the furnace and if you have a 2/wire going to R and G which is separate from your thermostat wiring (which should be R/G/W and maybe C and/or Y) than simply back off one of the R or G from that 2/wire if that solves the problem it's either the switch being on or a relay issue.

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