Need help troubleshooting Atwood furnace

[tallpall888]

This is the 8535 - IV DCLP on a 2006 Alfa 36 ft fifth wheeler. Furnace has worked fine since 2008 when we bought this used, but have not used the furnace very much spending our winters in South Texas and Florida so not much demand for the heat.
This year it would not start up after a chilly 55 degree evening. Could see the problem was a frozen motor, so ordered one and replaced it.
The motor and circuit board had gotten wet at some point in the past. This furnace is mounted vertically (long end up) so the bottom of the circuit board and the open end of the blower fan assy were exposed in an up position that allowed them to get wet by something. I'm guessing it was a cracked skylight assy which was near enough above it (over the shower) to be the culprit. It has been replaced.
Everything back together it now starts, ignites, blows warm air out the exhaust, then turns off. Three times. Ignition lockout is the failure code of the LED, three blinks then a pause.
I'm wondering why the thing thinks it's burner and blower is not operating correctly as it looks like it is to me. Is there something that detects proper or improper burner heat and lets the circuit board know?
Guess I'm looking for a reason other than a bad circuit board.

[tallpall888]

Good to know....I moved the spark/ignitor around a bit and now it it working. Thanks for the info!

Ken

[wlstroud]

Make sure the thermocouple/igniter is spaced correctly (1/8" I think). Re-gap the electrodes to 1/8" if too wide or too narrow. 3 flashes is lockout due to flame loss. If the thermocouple safety is not heated enough by the flame, it will cut off the gas. Your control board if probably OK.

[enblethen]

The ignitor doubles as a flame sensor. If not directly in the flame it will shut down the furnace.
Another item that could be causing issues is the ECO. If it detects that the fire box is getting too hot it will shut down the furnace.
Make sure there is a good 12 plus volts getting to the fan motor. Low speed can cause lower air flow and shut down via the sail switch.