Hello,
I have 10 year old bryant 80+ furnace and programmable thermostat which I replaced with new one to fix this problem. The furnace will work fine start and stop if I keep the temp at 63 degree. If I rase the temp to 65 degree it will not turn of and will keep running until you turn off te power.

Please let me know what I have to replace. I think thermostat is not the issu.

If I rase the temp to 65 degree it will not turn of and and will keep running until you turn off te power.

So are you saying that the unit keeps running till it gets to 90 degrees or that the unit will not heat the home up to 65 degrees.

During this running time is the burner on all the time or just the blower.

The furnace is on with burner and blower. It will continue running doesn't care the set temp and will not shut off. I have to turn off and on the power. It will have no problem at 63 degree it works normal. Turn on and turn off when it reaches the set temp 63.

If that is the case something has to be wrong with the thermostat since for some reason it wants to keep calling for heat after it is satisfied at the 63 degree set point.

To test the thermostat just disconnect the white (W) wire at the furnace. If the furnace burner stops running then you know it is the thermostat since it is still calling for heat after the set point..

I have replaced the thermostat and its same with the new one. I don't think its thermostat. What makes burner to turn off when it gets to the set temp.

It works fine when temp is set to 63 degree. If I change the temp to 67 degree the it does not turn off. Is there that furnace has to run longer to get to 67 and cause some condensation or temp sensor has issue?

What makes burner to turn off when it gets to the set temp.

The thermostat turns off the furnace.

It works fine when temp is set to 63 degree. If I change the temp to 67 degree the it does not turn off.

Where ever the thermostat is set to the furnace will turn off when it hits the temperature it is set to. Real simple. If this does not happen then something else is making the furnace run longer and the only thing I know of is the thermostat. Sorry

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Originally Posted by hvac1000

If I rase the temp to 65 degree it will not turn of and and will keep running until you turn off te power.

So are you saying that the unit keeps running till it gets to 90 degrees or that the unit will not heat the home up to 65 degrees.

During this running tiem is the burner on all the time or just the blower.

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Before you replaced the thermostat did the furnace have the same problem in the beginning. Disconect the thermostat from the base plate and see if the heater runs now.If it does then the problem is not the thermostat.

If you take the thermostat off its base the unit should not run if it does then the thermostat the problem.

1) How thermostat know that it reaches the set temprature, is there a temp sensor in the furnace.

2) Yes furnace have the same problem, that was the rason I change the thermostat

3) As I said the thermostat will work if the set temp is below 63 degree. After that I think furnace get locked and only you can turn off by turning off the power