RV Repair: suburban sf-25 furnace, wasp nest, burn cycle

Question
Shawn-
Fan runs,furnace ignites but burns for only 3 seconds or so, then repeats same ignition and burn cycle. I figured it was obstruction in air intake and did remove wasp nest, but problem persists. The burn is blue so I assume its getting good intake. Could it be there is more obstruction deeper in heat exchanger/exhaust? How can the exchanger chambers be cleaned further? Can I remove burner and flush with water? Can I rule out limit and sail switches since it ignites? Can it be the board? Thanks for your advice.

Answer
Hi Greg. You are on the way to being a great RV Tech! Yes! You can rule out the limit and sail. Blow compressed air through the chamber and see if you get good flow out the exhaust. If so. The chamber is fine. You most likely have a bad electrode or a bad board. Try the electrode first. (cheaper) If you still have the problem. Then replace the board. Good Luck