im having problems with my trane furnice. I noticed there was no flame in the piolit so i chanced the thermocoupler. I dont know what do do next. My next idea was to change the thermostat, but the Aircondition turns on, but the heater doesnt. I can also turn the blower on and it works. For some reason the heater will not turn on. What could be the reason?
If the furnace is less than ten years old, there is a led light on the control board. It will flash x number of times. The flashing light is a "tattle tale". somewhere on the board or the door panel, there is a legend that will indicate what the problem is by the number of flashes. At least that is a starting point in diagnosing the problem. There is no sense in replacing parts without having an idea what is wrong.
You mentioned a thermocouple. Is this an older furnace?