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?
Furnace won’t adjust to thermostat setting
furnaceheating
Related Solutions
I had the exact same symptoms with my natural gas furnace, and it turned out to be the flame sensor.
It's an L-shaped metal bar (but can also be straight, depending on model) that detects if there are flames actually coming out, and turns off the gas if not. It had a white high-temp wire connecting it to the control board. Taking it out, cleaning it with some steel wool fixed the problem for me.
If yours is like the above, you'll only see the back part of it and the bracket, as the L-shaped end is inside the heating unit.
Can you look at the furnace during the time it is blowing cold air and see if the flame is on?
The thermostat has the ability to control the fan, but typically the thermostat sends a "turn heat on" signal to the furnace and the furnace controls are setup to turn the flame on for a X amount of time (to warm up the air) and then turn on the fan once the timer expired (so the air coming out of the vents is not cold). When the heat is turned on is the flame and fan going on at the same time?
Not sure about your furnace, but some have a couple of LEDs that are lit up and can be used to read a status or error codes. If you have the manual you could try to decipher the code while the cold air is running and see if it gives you a clue.
I would start by trying to figure out if the problem is with the thermostat or the furnace by installing a new thermostat and seeing if the problem goes away. If the problem is still there you can just return it. I had a furnace issue where it was going off randomly and would work in heat mode but not cool mode. It turned out that the thermostat was bad and sending intermittent signals.
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Best Answer
Does the furnace shut down when the thermostat stops calling for heat (or very soon after)?
Furnace
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.
Thermostat
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.