In another post you have a photo of your furnace door. It has louvers that allow water to enter. Had the same problem until dealer replaced the furnace door. The new door has a gasket, almost like a liner to keep water out. It is a common problem :
http://www.thorforums.com/forums/f8/...16-a-5865.html
The parts are available from Thor, but it replaces the door, the frame, the exhaust tube and the exhaust plate. The new door has no louvers and attaches with 6 screws, not 4.
Thor Forums
