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I have a moncrief furnace and replaced the thermostat but the furnace will not cut off once it reaches the desired temperature. What could be wrong?

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so it just keeps heating and the temp keeps increasing? – Steven Nov 26 '12 at 21:07
How many degrees over the thermostat setpoint does it get up to? – littleturtle Nov 26 '12 at 21:19
In addition to the questions above: Did the problem start happening after replacing the thermostat, or did you replace the thermostat in an attempt to fix? What kind of thermostat was there before and what did you replace it with? Were the terminals/wires labelled and are you sure you reconnected them properly? (This may not be relevant, but:) Does the problem go away if you put the old thermostat back in? – gregmac Nov 26 '12 at 21:40
I'm downvoting until more detail is added to this question. In the current state, it qualifies as "not a real question" since we don't have enough information to provide a proper answer. – BMitch Nov 27 '12 at 12:55
When I removed and replaced the Honeywell thermostat from my boiler to fix the hot water coil I had the same problem. I found that when I pushed the copper probe into the crevice in the boiler it was not in all the way, and did not register the water temp. Once I made sure it was seated in the whole way it shut off at the correct threshold. – Bob A. Nov 28 '12 at 18:29

Home thermostats typically operate with a "dead band", a range above and below the set point that the furnace operates over. For example, if the setpoint is 68°F the furnace might turn on at 62°F and off at 71°F.

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