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Old 10-08-2018, 03:09 PM   #1
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Join Date: Aug 2013
Location: Cedar Rapids, IA
Posts: 13
Miramar 35.3 Furnace Issue

This query is specific to our 2018 Thor Miramar 35.3 coach but it may also apply to any RV using the Firefly Integrations wireless products for system controls e.g. lights, pumps, AC, etc.

Recently our furnace (Dometic aka Atwood AFMD35141) has been intermittent that is sometimes it ignites and sometimes not. Of course it goes into lockout mode after the third attempt.

Well to make a long story short I have checked all of the furnace functions i.e. sail and limit switches, gas valve, ignitor and circuit board and all to be working correctly. Also made sure no air was in the LP line, no obstructions on the interior vents and the tank regulator was in working order. In addition outside vent has a screened cover to keep out the flying critters.

I am beginning to wonder if the issue is with the Firefly Integrations G7A panel. The reason I say that is because we had issues with both of our ACs this summer. The solution was to completely reboot the G7A by shutting down all power i.e. 12 VDC and shore power, wait 30 seconds and reapply power. We have tried this same method for the furnace but did not correct the problem.

My question is hve any of you out there had a similar situation? We will probably end of taking it in for a service call but I am not sure they will be able to determine the root cause of the problem.
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Old 10-15-2018, 06:34 AM   #2
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Thor Owners Club
Ford Super Duty Owner
Join Date: Aug 2015
Location: IL
Posts: 119
It’s not the same issue but we had a couple of problems with rain getting in thru the vent and causing motherboard problems. Passing this along I’m case anyone else had similar experience.

We have a ‘16, 33.5.

Once, it was just “clicking” like it wanted to start but wouldn’t. Had to pull the fuse, repaired/replaced motherboard once home by dealer.

Second time, it wouldn’t shut off, had to disconnect the power, again repaired once home. Both times we were in heavy wind and rain.

Not clear what’s been changed by Thor to address.
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Old 10-15-2018, 01:12 PM   #3
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Quote:
Originally Posted by JD11 View Post
It’s not the same issue but we had a couple of problems with rain getting in thru the vent and causing motherboard problems.

I have had rain come in via the furnace twice. Both times were during a driving rain against the side of the Motorhome where the vent pipe is. After it had rained for awhile, I noticed a puddle coming out from under the fridge (the furnace is under the fridge in a Miramar 35.3). I pulled out the drawer that's near the floor under the stove and I could see water dripping out of the outside case of the furnace.



How did you fix your leak? When I went outside and unscrewed the 4 screws that hold in the vent and vent pipe, the pipe is angled down which would let water in. Not sure how to fix this.


Burch
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Old 10-15-2018, 02:04 PM   #4
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Join Date: Sep 2015
Location: Denver
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I've had similar problems with our Atwood heater. We have had the water on the board problem, with the symptom being that the air blower would run even without being commanded by the thermostat.

Last summer we had a problem with flame ignition. The flame would light, but wouldn't stabilize and shut off. After the third try, the controller would lock out further attempts.

I ended up buying a new gas valve as I was hearing solenoid chatter when the the flame would fail. The replacement valve seems to have fixed the flame stability problem.

I addressed the water on the board problem by drilling a few holes on the shelf upon which the board sits and also putting a non-conductive shim under the board to hold it a bit higher off the shelf. Atwood was little help. They do have a board relocation kit, but won't sell me one. I have to go to an "authorized service provider", as if Camping World could be trusted. I've also sealed the slot into which the cover fits with some rubber weather seal I had in my pile of bought but never used stuff. That seems to keep everything dry.
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Old 10-16-2018, 07:21 AM   #5
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Location: Cedar Rapids, IA
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35.3 Furnace Issue...

Thanks for the information. Yes we did have an extended period of wet weather here in eastern Iowa and some of it was wind driven. Looking through the grate under the refrigerator I did notice one can see light coming in around the outside furnace cover. Obviously not totally sealed but then again that seems to be true of many places on our RV. I suspect the same is true for others.

Anyway it would make sense that moisture could wreck havoc on the control board. I have to wonder if applying conformal coating on the board would help the situation. That is the method used by my previous employer to protect sensitive components and circuit boards used in avionic and communication equipment.

Sadly we have had t put our unit away for the winter (not yet there for full timing). But since we have had a period of extended dry weather I may try to see if the furnace works now before I remove the batteries for storage. Wish me luck.
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