Originally Posted by nosticks
Not so. It's very easy to replace the circuit board. Furnace does not need to be removed. Access panel on the outside is removed. Board unplugs. New board plugs in. There are led's on the board which will indicate the status of the board.
But, before you do anything, remove the access panel and blow dry the board with a hair dryer. My guess is condensation on the board.
I guess you have never seen a Suburban SF-30 heater. Very common heater. I have owned 2 of them. No exterior access. Intake and exhaust vents only. Requires inside removal. No DIY testing procedures. You need a a work bench. A gas supply. A 12 volt power supply. And aboard tester.