I've been having an intermittent problem with my furnace that no one has been able to figure out. The burner will come on and after reaching the required temperature, the thermostat shuts down, the burner goes off but the fan will continue to run and run and the room temperature will drop significantly. This usually happens in the middle of the night but not when the heating and cooling company is here. I have to get up, turn the thermostat down or off to stop the cold air from blowing. I have had the heating company out 5 times in the last month but they can't recreate the problem and have no idea whats wrong. Help!