Strange furnace problem

[ChuckBC]

With mine, this spring, I purchased 2 brand new sail switches and tried 1 that worked then did not work. Put in 2nd one and it has been working since. Only several outings out under belt and every time I go out to trailer I try with fingers crossed. Testing 1st one did seem to operate but playing paddle spring on microswitch it hung up a bit. Other seemed to have good on/off response. Mine unlike yours is the Atwood with larger square paddle face.

[davidmurphy02]

Well, I think I finally have my furnace problem resolved - looks like a faulty gas valve was the culprit. Having tried all the easier stuff first, and knowing that I had an ignition failure that was likely an igniter or gas valve problem, I decided to go ahead and replace the gas valve - not much left to try. The gas valve, igniter and burner are all one assembly that comes out together so although the igniter looked fine I went ahead and replaced it at the same time.

Previously when I stood outside the exhaust vent and listened during the ignition process I could hear the igniter clicking away furiously. If the burner doesn't ignite after five seconds it stops, blows air for 15 seconds and then tries again. Numerous times the burner would finally light on the second or third attempt, and in every case after several long seconds of the igniter clicking/sparking.

With the new gas valve installed, on the first attempt the burner lit IMMEDIATELY at the first click or two of the igniter. On several subsequent cycles it did the same thing - no problems or delays whatsoever with ignition. I suspect the old gas valve was just not letting enough gas through every time to produce ignition. There is a small brass orifice on the gas valve which I inspected but it did not appear to be dirty or obstructed. In fact, I had to transfer that orifice to the new gas valve and it works fine there. Hard to figure what was going wrong in the old gas valve, but anything can break or malfunction and that is apparently what happened here.

I realize not everyone would want to tackle replacing the furnace gas valve, but these days when RV repair shops are booked out for months if you are DIY inclined at all, it's really not a bad job. The gas line coming in from the top has some flex and once the fitting is loosened can be pushed up and off. There are a couple of wire connectors to remove, and then only 3 screws mounting the assembly to the furnace wall - although reaching them does require a long bit extension. I found that removing the lower exhaust pipe allowed more space to move the gas valve assembly around in working it in and out of the compartment.

One thing I will say for this furnace - with the exterior door, virtually all of the components that could ever need replacing can be accessed from the outside. It took about 45 minutes to replace the gas valve assembly. I had read that the gap in the igniter electrode should be 1/8" so just before installing the new assembly I adjusted the electrodes - in the photo below they look further apart than that.

If you have followed this thread since the beginning you know what an adventure this has been. In the process I've learned a lot about how the furnace works, how to diagnose problems, and how to replace a number of components. I plan to do a separate post compiling this info but without all the wailing about cold nights and frustration with attempts at fixes that did not work.

[brroberts]

Congratulations, and thanks for all of the updates to help others down the road.

[rubicon327]

Originally Posted by davidmurphy02

Well, I think I finally have my furnace problem resolved - looks like a faulty gas valve was the culprit. Having tried all the easier stuff first, and knowing that I had an ignition failure that was likely an igniter or gas valve problem, I decided to go ahead and replace the gas valve - not much left to try. The gas valve, igniter and burner are all one assembly that comes out together so although the igniter looked fine I went ahead and replaced it at the same time.

David: Glad to hear this intermittent furnace problem is most certainly behind you. You are now the resident expert on parts replacement for the Dometic DFSAD / Atwood AFSAD furnaces. Gas valve didn't even occur to me. I commend your tenacity to get to a resolution to this on your own. Sometimes our technical advice from 1700 miles away turns more into moral support but hopefully that still helped!

[Centex]

Originally Posted by brroberts

Congratulations, and thanks for all of the updates to help others down the road.

Originally Posted by rubicon327

David: Glad to hear this intermittent furnace problem is most certainly behind you. You are now the resident expert on parts replacement for the Dometic DFSAD / Atwood AFSAD furnaces. Gas valve didn't even occur to me. I commend your tenacity to get to a resolution to this on your own.

I'll 'second' all Randy and Dave said and add a third thumbs-up for you, David

[Rossue]

Yay & never give up!!

[Greatboatz3]

David, Congratulations! I have been following this post with a lot of interest. You are a inspiration.
Jim A.

[Melusine]

Chiming in: thanks for the stellar example of tenacity, David! Everybody's right when they say you are quite an inspiration, and your humorous approach to one of those "grrrrrrrr" situations doesn't hurt.
Best regards from
Jon & Jen in AZ

[WRGooding]

David we all should send you a beer. I never would have thought the gas valve.Thanks!

[Mike G]

Wow, congratulations! Now if you want to make some extra money, you could hire out as an RV furnace repairman (or even a consultant).


My home hot water heater needed a new gas valve this spring. Darn thing cost about $500 to replace, parts and labor. I think there's a computer chip in it.

[davidmurphy02]

Well, I thought I would post an update. We have been on the road since late September. Overnight lows in the 20's to 40's and have used the furnace just about every night, altitudes up to 7,000 feet. It has worked perfectly, the gas valve was definitely the culprit. Ignition is instant as soon as the gas valve clicks open.

I went ahead and replaced the insect screen I had over the interior opening to prevent cat hair from getting to the sail switch. I had replaced the flex duct with a smooth metal duct and replaced the metal grill cover with 1/2" hardware cloth painted black, now with the insect screen behind that. I can easily remove the wood panel to brush off the screen from time to time. It does not impede the air flow, if anything with the smooth duct and wire mesh cover the air flow is better.

It's so nice to be able to take a working furnace for granted again!

[rubicon327]

Originally Posted by davidmurphy02

It's so nice to be able to take a working furnace for granted again!

Thanks for the update. Glad it is working well. Even though we have the older, trusty Atwood 8012-II furnace we still carry a Mr. Buddy as a backup at times. Right now the trailer is set up as a off-grid fishing basecamp near Lake Erie. Wouldn't want to have to run the generator almost 24/7 for an electric heater or mini-split heat pump if propane furnace had a problem. When it is cold and you have an extended camping agenda it is never a bad idea to have an interim propane heating solution. Unfortunately it seems you can never get too comfortable with these darn RV furnaces!

[Perry Butler]

Originally Posted by rubicon327

Thanks for the update. Glad it is working well. Even though we have the older, trusty Atwood 8012-II furnace we still carry a Mr. Buddy as a backup at times. Right now the trailer is set up as a off-grid fishing basecamp near Lake Erie. Wouldn't want to have to run the generator almost 24/7 for an electric heater or mini-split heat pump if propane furnace had a problem. When it is cold and you have an extended camping agenda it is never a bad idea to have an interim propane heating solution. Unfortunately it seems you can never get too comfortable with these darn RV furnaces!

We had our sail switch fail at least 5 times on our six week inaugural trip from delivery at Sumas. Since then we have a Mr Buddy that is used all the time to quickly warm up the camper when we go in for the evening, and for use in cold shower areas so you don't freeze after finishing the shower.

We also have a Martin catalytic heater that can go down to 1,400 btu (vs 4,000 btu's for the Mr Buddy on low). It's been used quite a bit the past two years and catalytic heaters have a limited lifespan.

Enjoy,

Perry

[Tam2004]

Originally Posted by davidmurphy02

Well, I think I finally have my furnace problem resolved - looks like a faulty gas valve was the culprit.

We have so appreciated your efforts on sharing the furnace issues. We have had some harrowing times. This summer we replaced the sail switch -- just now after a cold trip to and from Colorado to visit 102 year old Aunt- we took ours into the shop and outlined symptoms that indicated several problems. I thought the gas valve might be an issue - but the shop said the gas valve was on back order and they doubted that anyway. They found problems with the fan controller (in the ceiling) and changed out the whole thermostat too -- also the limit switch. When it still had problems they changed out the control board with the better Dinosaur board. Since we don't have the skills of many of the other members - we paid out $538 and were OK with that. We now, due to all of you, will be able to change out our own control boards and sail switches AND as we test it over the coming weeks and if there is a problem with the gas valve we will know to get that done by Spring - maybe it will be in by then! Thanks everyone. The shop manager said that sadly replacing parts doesn't always work as the parts can be bad -- so we did a Dinosaur control board and kept our old one that may or may not be bad as a backup while we travel.

[Tam2004]

Update on furnace -- after the extensive fix on furnace I mention above - the fixes lasted 5 days - and the reluctance for our RV shop to replace the gas valve -- I just found a RV mobile service with a great guy willing to do what we want. So this is a bit of a "Hail Mary" attempt. The RV mobile guy said these Dometic furnaces have been a disaster for people -very touchy. One time he found the exhaust pipe was wrong (I doubt this is an Escape trailer issue) - but he is willing to let us spend our money for the small business economy and just give us a new gas valve and igniter (since David did this also). I will let you know if this turns out to solve our issues. Three years in and one of the best things we ever did was to buy a small buddy gas heater as backup (we have a electrical heater as back up for when in electrical sites.). FINGERS CROSSED. He will install in a few days.

[Eggscape]

Thanks for the update…always interested in what works and what doesn’t.

[Tam2004]

NEW THEORY!! Bill Hall Mobile RV servicer -- Bend OR -- 20 years experience with RV's and very aware of these flawed Dometic furnaces came out a few days ago. Much to his surprise - when I turned on the furnace inside and he was outside he saw sparks coming down to the lower left of the furnace door (closed door) - he did get to hear the current symptoms (blower comes on - 3 attempts to ignite with 10 plus seconds in between in ignition attempt) does not ignite furnace shuts off. Small smell of gas at first.

Bill said the circuit board was throwing a spark that hits the metal door and scatters. He took a few minutes to cut some insulation to put over the board that is just a 4" part of a plastic bottle. The furnace has worked for several days now - but he and I am thinking over time the insulation could thin so we might seek another more sturdy solution.

I have a message into Escape to talk about this - do they have a better work around. He said some are turning to plastic doors to cover the furnaces to mitigate this spark from coil and metal door. We are wondering if he found one of the serious flaws with this furnace = along with the sail switch which he said is a hopelessly bad design and install. I intend to keep working on this - Dometic support is hopeless. He did not think it was our gas valve or igniter, but will be able to do this if needed.

[davidmurphy02]

Very interesting - seems there is no end to weird furnace issues. I had tried replacing the circuit board with an OEM board and then a Dinosaur board to no effect, and since replacing the gas valve it has worked flawlessly so I'm pretty sure that was my problem. But for sure sparks coming off the igniter coil are a bad thing - hope that turns out to resolve your problem.

[Mike G]

What years did ETI install Dometic furnaces? They're putting in (quieter) Atwood furnaces now, aren't they? Or is my memory going south?

[davidmurphy02]

Atwood was bought out by Dometic about 3 years ago, same furnaces.