I have a 2007 Trane furnace that has been working the AC all summer just fine. With the cooler weather, when I turn on the heat and set the thermostat to 72 degrees, the furnace comes on but heats the house to 82 degrees. When I put the thermostat back on cool and set the temperature, the cool air works fine. Why won't my furnace adjust to the heat temperature set at the thermostat but will work with the cool setting? Is it a problem with the thermostat? Or is there a heat sensor problem? Can anyone help?
Does the furnace shut down when the thermostat stops calling for heat (or very soon after)?
If the furnace does not shut down when the thermostat stops calling for heat, it's a problem with the furnace. It likely won't stop immediately, but should stop fairly soon after.
If the thermostat does not stop calling for heat once the set point is reached, it's a problem with the thermostat. Usually there is some form of indicator on the thermostat, that lets you know when it's calling for heat.
Read the manual for the thermostat, and make sure you're programming it properly.