furnace

I had the same problem on mu 2016 Bounder...I ended up taking the outside cover off and seeing the indentations on the foam gasket on the cover, I purchased some 1/4' peel 'em stick 'em weather stripping and installed OVER the indentations. Reinstalled the cover and no more issue, and we have been thru some heavy downpours. Hope this may help you!

I have the same problem with an Atwood in a 2016 Thor ACE. Furnace works fine until it rains. The cover on the exhaust pipe has holes on the top (assume for air intake) that are large enough to let in a lot of rain if it is blowing hard. I can see the wiring through the holes. Don't see how you can block that off, but have to stop the rain from getting in somehow.

What is the model number?

Npoe mine has 4 screws. There is an inner gasket surrounding the fan and circuit board. , but still got water.

Some Atwoods have a plastic inner door that should protect the interior from rain intrusion.
If this is not there or not sealing properly, you could make a deflector out of a gallon milk jug. Cut a peice out of the side and attach over the left side to protect the circuit board and fan inlet. It needs to be one upper portion so as to not restrict air intack.
This is of course yours has the exterior door with two screws like the 8900.

it's an Atwood.my is 2013 coachman. Still raining here. So I will check caulking and gaskets. The blower was blowing water onto circuit board.

Moved from Forum Technical Support

If you post make and model of furnace, someone here maybe able to help with some type of rain deflector.
Sounds like a Atwood or Hydro-flame furnace.

just came in from the rain. Had my awning out helped some. Took cover off furnace and found water in compartment. When blower came on it was blowing water on circuit board. Causing unit to trip off. I was LUCKY that I circuit board didn't short out. Now I just have to figure how water got in. We are having a lot of rain and high winds.I used a hair dryer to dry up water, risked shocking myself, but I got furnace working.Something to file in problem solving.

I've experienced a similar thing with my water heater. Don't know if it's dust or cobwebs, but a blast from a can of air, like you use on a computer, and problem solved. No idea if this applies to your furnace issue but it's worth a shot before digging into its parts. It could blow off moisture if that's the problem. Just a thought.