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Old 01-26-2023, 10:25 AM   #1
In2b8r
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Wet Furnace circuit Board

After a lot of head scratching I opted to tear into the furnace to figure our why I had no - anything. No Heat, no fan, no power.... I took off the furnace access cover on my 2017 3820FK and went to 'diagnosing' the problem. Well call me a genius but it only took about 2 seconds to recognize that the circuit board should not be partially submerged in water. We hadn't had rain in some time (we are a permanent site camper) and I hadn't washed the camper for several weeks. The water issue has been going on for some time as the red wire connected to the circuit board (I believe that is the power from the thermostat) was totally rusted off of the board. Now that I identified the problem my question is what is the solution? I can replace the board but will most likely have the same issue (?) Where is the water coming from (?) I can enhance the seal on the furnace cover door but I am not convinced that is where the water is coming in. On this camper model the Furnace sits directly below the Hot Water tank - I don't seem to have a leak, but wondering if on those cool nights I am having a condensation issue(?) Is this a known issue and what if anything can be done to prevent a reoccurrence of this situation (?)
 
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Old 01-26-2023, 11:05 AM   #2
MandK
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I thought I read a post here or possibly on another forum of someone with the same problem. They called Dometic and Dometic sent them a plastic holder that holds the board up off the bottom of the furnace. Apparently there may have been a problem with the boards on some units sitting in water if the outside cover leaks. I believe the post also stated that it was a known problem and Dometic sent a new board at no cost.
I know that on my furnace, the board is mounted to a plastic holder via “Christmas tree” type pins. There is also a small open spot on the bottom of the cover that does not seal against the frame opening for water to drain out should any get in.
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Old 01-27-2023, 02:23 PM   #3
Bourbon County
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The fact that Dometic actually makes a plastic holder is itself troubling! These furnaces are a mini version of a condensing type burner found in residential furnaces. They draw in outdoor air for combustion and in the heating process will create condensate. I suspect this is the source of the water and the designers at Dometic didn't incorporate a system to drain it.

It might not help, but certainly can't hurt is a little maintenance on your furnace. Remove the outer cover and check the air inlet and exhaust ports. These are notorious havens for insects that build nests in there during warmer months. Take a shop vac and maybe a bottle brush and clean them out completely. As short as the exhaust tube is, it should be able to push the moisture out before it starts to condense; but if it's partially blocked it might not be able to.
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Old 01-27-2023, 03:07 PM   #4
Daryles
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I made a hood to go over the exhaust vent. Helps deflect rain away.
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Old 01-27-2023, 03:19 PM   #5
Mikendebbie
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Quote:
Originally Posted by Daryles View Post
I made a hood to go over the exhaust vent. Helps deflect rain away.
Daryles - does that thing ride there all the time or do you take it off for travel?
How is it mounted?
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Old 01-27-2023, 04:15 PM   #6
Daryles
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Originally Posted by Mikendebbie View Post
Daryles - does that thing ride there all the time or do you take it off for travel?
How is it mounted?
It stays on all the time. It's held on by the 4 screws on the exhaust vent plate.
I made a template out of paper to get the angles right, then traced it onto some aluminum flashing.
Drilled mounting holes, folded it, painted it, mounted it.
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Old 02-01-2023, 02:47 PM   #7
DanandBrenda
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Quote:
Originally Posted by In2b8r View Post
After a lot of head scratching I opted to tear into the furnace to figure our why I had no - anything. No Heat, no fan, no power.... I took off the furnace access cover on my 2017 3820FK and went to 'diagnosing' the problem. Well call me a genius but it only took about 2 seconds to recognize that the circuit board should not be partially submerged in water. We hadn't had rain in some time (we are a permanent site camper) and I hadn't washed the camper for several weeks. The water issue has been going on for some time as the red wire connected to the circuit board (I believe that is the power from the thermostat) was totally rusted off of the board. Now that I identified the problem my question is what is the solution? I can replace the board but will most likely have the same issue (?) Where is the water coming from (?) I can enhance the seal on the furnace cover door but I am not convinced that is where the water is coming in. On this camper model the Furnace sits directly below the Hot Water tank - I don't seem to have a leak, but wondering if on those cool nights I am having a condensation issue(?) Is this a known issue and what if anything can be done to prevent a reoccurrence of this situation (?)
Mine did the same thing turns out it was the seal on the plastic cover. I replaced the circuit board twice before I figure out what was causing the water to get in.
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