[Montajmahal]

Went to turn on our furnace for the 1st time this year. The fan came on for about a minute, no DSI spark, shut down, cycled again and finally a lock out, 3 blinks on the board. Reset it, turned it on again and went outside this time. Heard gargling water, same result. If not for the water sound I would suspect the sail switch, high limit switch, then the board, but after taking the unit out and removing the burner / gas valve / ignitor assembly I found a whole bunch of rusty water. There was no water present when I initially took the cover off, except when I discovered the water sound there was drips of water being blown out from the squirrel cage fan, and no water anywhere near the furnace inside. Therefore I concluded water entered the unit through the exhaust vent. This unit is mounted vertically by the way (3791RD). What amazes me is how much water got into the burn chamber, and that the fan creates enough CFM to pull water all the way through the furnace internal tubing (where it would have to elevate twice) to destroy the burner assembly. I replaced the burner and ignition assembly, cleaned things up, and it now fires right up and is functioning normally. The gas valve was also fine.

So, my next thought is the design of this vertical furnace with the S shaped exhaust pipe is ridicules and it needs some kind of vent cover, a dryer vent perhaps, to keep rain water out. We are in south Florida, and it rains more here than where I spent the last 30 years in Oregon, but I’ve never had this issue in any of my many RV’s in the last 40 years.

Any exhaust vent cover ideas? Anyone else experience this?

BTW, Dometic denied my claim and called it a Keystone installation issue, not mounted level. It’s mounted level.