"Occasionally", the furnace will shut down after thermostat request is satisfied AND the main blower will run continuously ( just like the thermostat was set for "continuous run". It will run until the thermostat asks for another burn cycle. After this cycle completes the unit MAY shut down exactly as it should. Any ideas as to what this could be? I have cleaned and re-seated all electrical connections to both the control box and the ignition control module; still doing it! Any help greatly appreciated! Steve Williams