
Originally Posted by
bryjcom
Sounds like you maybe lost a ground to the common side of the transformer. The behavior you describe sounds like a dirty flames sensor but since you've cleaned it, it probably isn't that. I've seen a faulty wiring harness cause the same issue. I've also seen a customer change out a transformer and not ground the common which caused the issue.
Run a wire from the C terminal on the board to a screw holding the board assembly to the furnace.
Ace hardware will most likely NOT have a flame sensor.