Atwood auto ignition ignites with force and blows flame out

by Stan Soth
(San Diego)

My 15 year old, 10 gallon, Atwood water heater lights when I turn it on with the switch inside my coach and heats the water. However, when we use some hot water and the temperature goes low enough for the thermostat to relight the heater, the resulting ignition occurs with such force (like a mini explosion) that it blows the flame out and the computer shuts it down.

If I cycle the switch, it usually lights and heats back up. I have cleaned the burner tube, nozzle and flue tube with no improvement. I have adjusted the spark gap and position and ruled out shorts. The flame spreader is positioned properly.