Water getting onto the furnace circuit board. I had the same problem multiple times after rain. Searching this and other forums will result in lots of posts on this common problem. When I first called Thor about this, they got Atwood on the phone and sent me a new board, which proved to be unnecessary as the problem re-occurred with the new board. Drying out the board fixed the problem until the next rain.
Atwood doesnít properly seal their covers and located the control board horizontally over a plastic shelf that holds water. Very bad design. They have a board relocation kit, but wouldnít sell me one - they said Iíd have to go to an authorized dealer to get one installed. If you are under warranty will will cost only the time and the cost of getting to an authorized dealer. My authorized dealer was a Camping World which was an unpalatable solution.
I ended up getting some rubber door seal and putting it into the slot where the cover flange goes. Also drilled a few holes in the plastic shelf To prevent accumulation of water. Problem appears to be solved as itís been over a year with no issues.
Seal is something like this
Attached picture shows the installed weatherstrip. There are still remnants of a temporary campground attempted fix with silicon sealer which didnít work.