My furnace will work fine all day most times and then shut off byself I find 3 blinking leds. I usually wake up in the morning with furnace not turning with setback thermo calling and also find that 3 blinking leds.I turn off frnace to reset.I just replaced induced draft fan which was definitely defective.I tried shorting out wire to pressure switch to see if pressure switch was defective and unit wouldn't start.Is there a sequence of being open and closing at sometime inteerval.I removed wires from switch and unit went off and immediately reconnected switch and furnace ran normal with out resetting and it continued to run so just opening circuit to switch momentarily don't cause a malfunction.will a cracked heat exchanger cause this problem.someone had said that goodman gmps are prone to cracked heat exchanges and how can one check for a cracked heat exchange. Looking forward to some help
Thanks Paul