[Stimus]

Hello,

I have a Heil SP80 natural gas induced draft fan furnace, model # NUG5075BFB2. The unit fires up normally and all is well until the unit shuts off when the temperature setpoint is reached.

The draft inducer motor then cycles on and off shortly after the flame is shut down and for 20 or more cycles at a pattern of 3-4 seconds between the motor on and off states. This continues during and after the main blower timed cool down operation.

I hear a series of clicks in the pressure switch and pinching the vacuum line shut has no effect on the cycling. What should I look for?

Thanks!
Bill

[Stimus]

OK, I vacuumed the furnace interior and pulled all electrical connectors one by one and sprayed on some DeoxIT D5 contact cleaner.

The cycling appears to have stopped so so far so good. Will order a backup igniter/flame sensor assembly since the original is now over 14 years old and my research indicates that this is the next item to likely need replacing.

Up to this event, this furnace has been troublefree since I bought the house in 1998 (furnace replaced with current unit around 1995) so I am pleased with Heil furnaces so far. I lube the blower motor every 2 years and keep clean filters in place. The unit is in a hallway closet so it is easy to access and is not exposed to a hostile environment such as crawlspaces and attics.