I have a Lennox WhisperHeat G20 series furnace. I had two problems. One was a noisy motor, oiling did not address it - that was easy, I put a new motor in and all was well there. The second problem is proving more challenging; The furnace will not come on automatically in the heat setting. It will for the a/c. First thought was to replace the thermostat but that did not sort out the problem. The next thought was to replace the circuit board. That did not sort it out either and now I'm stumped. having replaced the motor (& capacitor), the thermostat and the circuit board there doesn't seem to be much left to repair or replace.