OK, last winter our furnace stopped working. We called in repairmen and they fixed it. Then a month later, when we'd turn it on, you could hear it start up but it wouldn't blow any air out. They came back and fixed it by replacing the thermostat which they said was wired wrong. No trouble all summer/fall. Now it is winter again and the furnace is doing the same thing= Turn it on and you can see the burner light up, you can hear the fan "HHHHMMMMMMMMMing" but no air comes out and after a couple minutes it shuts off, then in a couple more minutes, it tries again. Over and over. If I shut it off, and leave it off for a few hours and then turn it back on, it comes on and heats right up no problem. And then after 2-3 hours it starts the no air nonsense again.