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Old 02-16-2020, 10:54 AM   #1
Montajmahal
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Dometic / Atwood furnace waterlogged

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.
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Old 02-16-2020, 02:18 PM   #2
DutchmenSport
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Condensation over time? Hot furnace, hot metal, cool air around it equals...condensation???
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Old 02-16-2020, 02:50 PM   #3
Montajmahal
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The furnace hasn’t been run since last winter. All the water was contained within the burner tubing. Everything else was bone dry, no condensation present. Except for a couple days, it has been very warm here in S. Florida. It had to have collected rain water, and there was a lot of it.
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Old 05-20-2020, 06:30 AM   #4
Leyland
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I have a 3791 RD and have had the exact issue. What did you do to resolve your issue. I have been thinking about a cover shield (awning type metal hood) over the discharge vent. Don’t know if this is the fix or not. Your pics are exact luck like mine for the burner and little orfice.
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Old 05-20-2020, 11:47 AM   #5
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The water issue for most of us has been leaks around the plastic cover when subjected to heavy wind and rain. The solution for me was to seal the top 3/4 with butal tape. No problems since.
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Old 05-20-2020, 12:36 PM   #6
Leyland
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Is the water coming in from the big plastic cover or they the hot exhaust air discharge ? When I looked at mine, I don’t see how the water got into the burner part with out coming in thru the discharge port.
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Old 05-20-2020, 12:40 PM   #7
Montajmahal
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Yes, the covers have historically allowed water to get in because the gasket behind them wasn’t making full contact, and also the screws are easily stripped. I had my cover replaced under warranty before I even took the house home. It was a known issue. I also replaced the screws with larger and longer versions.

Having said that, the cover was not the issue with mine after I replaced it. The way the exhaust tube is bent, water is allowed to enter the tube and water, a lot of it, was inside the furnace itself. There was no water present to be seen after taking the cover off at all. It was all inside the unit.

So, I have seen a great deal of units come in the shop ( I was a service manager ) with household type clothes dryer vents installed on top of the exhaust. Most were installed too high to do much if the rain is blowing sideways against the furnace, like it tends to do here in south Florida in the summer. I looked at various types including louvered metal ones. Whatever you do don’t use plastic. I will probably end up making my own. One that will cover the exhaust well enough but will allow the heat from the running furnace to exit safely.

In the mean time, because there is only about 30 days in the winter here that I would even use the furnace, and it hardly rains in that time, I simply covered the exhaust with clear plastic-
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Old 05-20-2020, 01:04 PM   #8
Montajmahal
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Quote:
Originally Posted by Leyland View Post
Is the water coming in from the big plastic cover or they the hot exhaust air discharge ? When I looked at mine, I don’t see how the water got into the burner part with out coming in thru the discharge port.
Exactly. The water in mine came in thru the hot air discharge port as you put it. No water anywhere else was found except INSIDE the furnace itself and made its way the the burner. I could hear water gargling inside the unit when I first discovered the issue. One of my techs master certified since 1999 was as surprised as I was, but it’s the only way water could get in.

Dometic didn’t dispute water can get in that way but blamed Keystone for installing the furnace on a tilt. It isn’t.
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Old 05-20-2020, 01:10 PM   #9
Leyland
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That exactly what I was thinking as well. I will have to look and see if I can find a dryer vent hood that I can use of get one fabricated. If anyone else has done this please post pics.
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Old 05-20-2020, 03:18 PM   #10
Harrisden54
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I had the exact same problem. Water entering through the exhaust tube. Dometic is familiar with the problem with the vertically mounted furnaces and replaced the rusted burner parts for free, but had no solution to prevent it from happening again. I bought a metal dryer vent cover at Home Depot and installed it over the exhaust to prevent the water from getting in. This worked but wasn't very pretty. When at the Goshen Rally last September, I spoke to the techs about it and they removed the dryer vent cover and caulked around the outer edges of the rectangular portion of the exhaust flange. This has seemed to work as I have been through several heavy rains since then. I've attached a few photos of the original repair that I ended up removing when I caulked the flange.
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File Type: jpg 20190703_102811.jpg (279.7 KB, 3 views)
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