Strange Furnace Problem

[ThomasC]

My 25-foot rear twin BigFoot has a strange furnace problem. I got home to Massachusetts late last March and my furnace promptly failed. I knew about the sail switch and little else. So, I watched some videos and looked at the wiring diagram which is quite simple.

All it has is a gas valve, igniter, fan, circuit board, and a couple of switches. The switches are in series. They are a sail switch which senses whether the fan is running and a temperature limit switch which will open if it gets too hot. So, if either switch opens the furnace will shut down.

I got out my ohm-meter and found almost 10 ohms in the limit switch. I found one at a RV dealer and replaced it. Easy fix. I ordered a circuit board and a sail switch to have spares but I couldn't find another limit switch right away. I remeasured the faulty limit switch and it came in at 0 ohms like a new one. Did it fix itself?

Well, it has started to get cold and the furnace failed again. The limit switch was about 7 ohms. So, I installed the old self-healing one and ordered a couple of new ones. I have heat and everything is fine. The new ones come in and I start ohm checking everything. Well, the second faulty one healed itself and has a zero-ohm reading now.

Don't you just love electronics. If this was an old-fashioned Bi-metal switch this wouldn't be happening. I left the first resurrected switch in there and we will see where this goes.

[David Tilston]

I hate gremlins.

[ThomasC]

Originally Posted by David Tilston

I hate gremlins.

Yeah this thing is a 2020. Is my furnace going to be problematic all of the time?

[Perryb67]

Originally Posted by ThomasC

Yeah this thing is a 2020. Is my furnace going to be problematic all of the time?

Sail switch problems in the first three months of ownership of our Escape 5.0 caused us to purchase a Martin catalytic heater that is 2,800 btu's on high and about 1,400 btu's on low. It keeps our Escape at about 50-60 F all night in cold weather (<40 F).

Yes, we purchased a second CO detector, always have the MaxxFan open a half inch, and open another window 1/4" when running the Martin so there is plenty of ventilation. We use it quite often since it's quiet and efficient, way more efficient than our furnace. If you don't understand the chemistry involved here don't use one, but for those who do it's great!

We have friends who have multiple sail switches, replaced a circuit board and carry a spare, and had to replace their gas solenoid valve (they probably have a spare valve as well). Those Dometic furnaces are not exactly state-of-the-art.

We also carry a Mr Buddy to warm up the camper when we get in at night with the outside temp at 40 F or less. Takes about 15 minutes to warm the camper, but the Buddy is just too hot (4,000 btu's) to use all night.

Enjoy,

Perry

[ThomasC]

Originally Posted by Perryb67

Sail switch problems in the first three months of ownership of our Escape 5.0 caused us to purchase a Martin catalytic heater that is 2,800 btu's on high and about 1,400 btu's on low. It keeps our Escape at about 50-60 F all night in cold weather (<40 F).

Yes, we purchased a second CO detector, always have the MaxxFan open a half inch, and open another window 1/4" when running the Martin so there is plenty of ventilation. We use it quite often since it's quiet and efficient, way more efficient than our furnace. If you don't understand the chemistry involved here don't use one, but for those who do it's great!

We have friends who have multiple sail switches, replaced a circuit board and carry a spare, and had to replace their gas solenoid valve (they probably have a spare valve as well). Those Dometic furnaces are not exactly state-of-the-art.

We also carry a Mr Buddy to warm up the camper when we get in at night with the outside temp at 40 F or less. Takes about 15 minutes to warm the camper, but the Buddy is just too hot (4,000 btu's) to use all night.

Enjoy,

Perry

The BigFoot furnace also heats the plumbing and tanks. If you have too much alternative heat available you could freeze your pipes.

[Perryb67]

Originally Posted by ThomasC

The BigFoot furnace also heats the plumbing and tanks. If you have too much alternative heat available you could freeze your pipes.

Good point! Being a former Bigfoot owner I should have remembered.

OTOH, at 25 F and above I'd have no problems using the Martin, in fact we've had many nights in our Escape with the nighttime temps down to 15 F and nothing's frozen (yet). Below 15 I usually use my air compressor to blow the lines clear and drain the fresh/grey water tanks. Our black water tank is in the camper.

Enjoy,

Perry

[Derek Johnson]

I had a problem where the furnace would occasionally decide not to turn on. After trying many different things I finally found the problem when I wiggled some wires and it turned on. There was a bad connection at the quick-splice that is staring you in the face when you open the outside cover.

[Moots]

We have a 2020 25RQ Bigfoot and are also having furnace issues, especially at higher elevations. Wish I had an answer.

[ThomasC]

Originally Posted by Moots

We have a 2020 25RQ Bigfoot and are also having furnace issues, especially at higher elevations. Wish I had an answer.

I think I have figured it out. I just haven't posted because it will be a long post and there are modified photos involved. I'm just a little lazy. Could you give some details of the problems I might be able to help now.

I think my problem was restrictions in the air flow. Like having anything in front of a vent even a little bit.

[Moots]

We have been pretty careful about putting anything in front of the air intake.

We live in CO and when we first went above 7,000 feet (when the BF was brand new), we couldn't get the furnace to light at all. It would cycle all night long if we would let it. Then we replaced the sail switch. That helped. Now the furnace will light (eventually) even at high elevations, but when it takes five our six cycles to light, it doesn't inspire much confidence for cold weather camping.

We have a solar installation and have an inverter and lithium battery located close to the furnace under the seat cushions. I have frequently wondered if we have crowded the furnace too much for it to function properly. However, when I search online, I read that a number of people have had problems at high elevations with these Dometic furnaces.

I've read your posts before and you are very good at diagnosing and solving problems. I am less so. We have an appointment in December with a fellow who is pretty handy with these furnaces. Hoping he can locate our issue. If he figures it out, we will post our solution.

[ThomasC]

Originally Posted by Moots

We have been pretty careful about putting anything in front of the air intake.

We live in CO and when we first went above 7,000 feet (when the BF was brand new), we couldn't get the furnace to light at all. It would cycle all night long if we would let it. Then we replaced the sail switch. That helped. Now the furnace will light (eventually) even at high elevations, but when it takes five our six cycles to light, it doesn't inspire much confidence for cold weather camping.

We have a solar installation and have an inverter and lithium battery located close to the furnace under the seat cushions. I have frequently wondered if we have crowded the furnace too much for it to function properly. However, when I search online, I read that a number of people have had problems at high elevations with these Dometic furnaces.

I've read your posts before and you are very good at diagnosing and solving problems. I am less so. We have an appointment in December with a fellow who is pretty handy with these furnaces. Hoping he can locate our issue. If he figures it out, we will post our solution.

You should have some information that came with the RV on the furnace. There is a led on the circuit board that will blink out several codes depending on what is going on. You have to remove the outside cover and at my age get down on my hands and knees and look up to see it.

There is a limit switch over the exhaust pipe but it is hard to get at. I have some extra-long needle nose pliers to get the wires off. Mine were originally a little loose, so I carefully tightened them with a pliers.

The first time I had problems the quilt was hanging in front of the bedroom vent. I corrected that because the bedroom felt cold. The furnace was also shutting down. The second time I put a 6-pack of Coke in the doorway that kind of blocked that vent.

My blink code said limit switch or air restriction. I am thinking it was the 6-pack that was in the way. It would crop up on colder nights when the furnace had to work harder and get warmer and maybe hot enough to trip the limit switch. It would shut down then retry in an hour. By then it had cooled and would work a while then repeat. I replaced the limit switch yet again even though I think it is alright and I moved the Coke. It has been good for a week.

High altitude,,, there is less air so it would burn rich but it should burn. I wonder if the thin air makes the sail switch iffy. Did you get your BigFoot from Denver. They are a mile high maybe they know. If you didn't get it there, I could call next week for you. Let me know.

[Moots]

Happy Thanksgiving, and what a thoughtful reply.

You have given us some good things to consider and look into. Thank you!

We know Dave and Jordan at Trailer World Denver well. Great people!

We actually bought our BF from British Columbia because Trailer World was sold out. Get Away RV had to pull our trailer to the U.S. border because we couldn't cross into Canada at the time because of Covid.

Thank you.

[ThomasC]

I finally fixed the furnace. Yeah maybe! I have said that to myself a few times in the past year. This time I am more confidant though.

I have a heat pump in my AC unit so if I had a furnace failure, I was OK as long as I was connected to shore power. So naturally the furnace only seemed to fail when I was on the road.

Every time I did something it would work for a while, and I would think it was fixed. I was fooled time and time again. I am Very good at fixing things. Except toasters, right now the score is toasters 3 and Tom zero.

I did a lot of reading online for information. I found a great thread over on the escape forum. I will leave the link and give you a chance to look it over because it seemed I was heading down the same road.

https://www.escapeforum.org/forums/f...lem-20418.html

I will try to post another chapter tonight.....Tom C.

[CharlesinGA]

I will be watching this. I know how hard it is to get a technical post right to where the non-technical person can make sense of it, along with the techies.......... take your time.

Charles

[ThomasC]

The furnace usually worked. I kept the vents free, and it was working pretty well. I had a spare circuit board, sail switch, and a few High temp shut off switches.

That guy from the escape forum ultimately fixed his with a gas valve. I didn't want to do that as it looked like a real pain, and I can't see where mine is bad. I left the sail switch in place and tested with my DMM (Digital Multi Meter). It was always fine.

Here is a photo of the offending unit.

[ThomasC]

The igniter is hiding behind the red wire. It is held in place with one screw after you slide it into a slot. You need a long-handled needle nose pliers for that.

The high temp shut off is way in the back above the exhaust pipe. That needle nose is needed again.

Finally, there is a nasty gromet that seals the gas line where it enters the unit. It interferes with your vision, and it is a problem to get in and out. I got pretty good at it after a few tries. A little siicone spray lube and that needle nose plus with a second pliers I learned how to wind it in and out.

here are a few more photos.

[ThomasC]

I have a heat pump in my AC unit and the weather was getting better so the heat was not needed as much. The unit was getting worse though, so a resolution was needed.

Around this time, I was working in my Morton building installing radiant heat. My electricity comes through that building, and I had to switch off of shore power and go to solar and battery.

I switched my refrigerator and hot water heater to propane when I did this. When I was using some hot water, I could hear my water heater failing to light up just like the furnace. I was excited thinking I had a propane problem, and maybe I could fix the furnace by solving the propane problem.

Here are a few pictures of the radiant heat install. I was starting to think that I had no business doing this if I couldn't fix a simple RV.

[ThomasC]

I lowered the water heater cover and looked for the usual. There were no blockages spiderwebs or anything in the line of the gas flow. I had nothing to test my regulator, but I turned off the two tanks then turned on just one. I turned on all three burners on my stove top. That was ok.

Then I did the same with the other tank. That was OK too. I tried to restart my hot water heater, and now it is working. That is weird. Time for some research. It seems you can reset a propane regulator. I accidently did that when I was switching from tank to tank.

I never heard of such a thing. You could have knocked me over with a feather. Check out this video.

https://www.youtube.com/watch?v=sJ6lyWQf_ow

[AlanKilian]

I always thought the flow regulator was in the tank and not in the regulator.

I don't think there's a need to remove the regulator. Every time this happened to me I just turned the tank off, gave it a little tap and then slowly turned it back on again and everything was fine.

https://www.youtube.com/watch?v=oaoI4frvhSQ

[ThomasC]

I did a lot of reading propane pressure. I have one of those connectors on the side of the RV to connect a BBQ grill. Now I know I need to have 11 inches of water column for all of your appliances

Time to build a manometer.

https://www.youtube.com/watch?v=QnlfQK-8qy4

I tried to find one that wasn't annoying, but they were all kind of bad. I found that I had less than 6 inches of water column. Half of what I was supposed to have. This must be my furnace problem.

I went to my local welding gas supply store and bought a new regulator. The old one is on the left side.