I have an ACE29.3.
The problem was the control board is on the bottom of the cabinet and is getting wet in heavy rain.
Now, the manufacturer of the furnace will not admit there is anything wrong.
We had this problem for two years, were about to sell the coach and take a loss.
One final try recently, someone from the dealership, no longer under warranty, and I called Thor. One conversation was enlightening. The Thor rep knew right away what I was talking about and said there is a relocation kit for the control board, it has a new board and bracket to get it off the ground. Contacting the vendor, of course they say there is no problem, but, you can order the relocation kit. Even though there is nothing wrong they have a kit to fix it. SMH.
Anyway, installed that today. Itís been an experience to get a solution but at least we have one. I hope this helps.
Here are the directions for it.