Furnace backfires from exhaust vent

[Star Dreamer]

3 hours ago, Jinx & Wayne said:

He's tried everywhere around here.  Do you have a dealer near you that can provide one?

Wayne & Jinx
2017 F-350 diesel, dually
2006 Carriage Carri-Lite 36KSQ

I have this horizontal regulator I took off our trailer to go with an auto switchover regulator for dual tanks. It is about a year old. We are in SC and will be heading to Florida in January if you want it

Edited December 7, 2021 by Star Dreamer

[Jinx & Wayne]

 

Thanks podwerkz.  I spoke to him yesterday and he finally got a regulator through a friend  back home.

On 12/7/2021 at 9:47 AM, podwerkz said:

And of course the one you need will probably not be in stock anywhere

 

Wayne & Jinx
2017 F-350 diesel, dually
2006 Carriage Carri-Lite 36KSQ

 

[odigity]

I just came here to ask for help with my backfiring furnace, and this thread was at the top of the forum.  That's funny.

I made a video of it:

No idea what to do.  I'm not very mechanically inclined.  Don't even know the model #, just that it's Dometic, because the manual lists 13 different model numbers.

[D&J]

49 minutes ago, odigity said:

I just came here to ask for help with my backfiring furnace, and this thread was at the top of the forum.  That's funny.

I made a video of it:

No idea what to do.  I'm not very mechanically inclined.  Don't even know the model #, just that it's Dometic, because the manual lists 13 different model numbers.

That is caused by a hole in the heat exchanger. Find a RV tech to confirm, if the rest of the furnace is in good shape they can replace the exchanger.

Denny

[Kirk W]

32 minutes ago, odigity said:

I made a video of it:

If I were you, I would get it checked by someone qualified before I used it again. To know the model you need to open the outside access panel and look inside for a plate that will tell you the model that you have. You can read through the thread thus far but if you are not sure how to do the suggested things you should probably get help. Before you do anything else, open that access and use a shop vacuum to clean the burner area. 

[odigity]

12 minutes ago, D&J said:

That is caused by a hole in the heat exchanger. Find a RV tech to confirm, if the rest of the furnace is in good shape they can replace the exchanger.

Thanks for the tip - I'll add it to my notes.

2 minutes ago, Kirk W said:

If I were you, I would get it checked by someone qualified before I used it again. To know the model you need to open the outside access panel and look inside for a plate that will tell you the model that you have. You can read through the thread thus far but if you are not sure how to do the suggested things you should probably get help. Before you do anything else, open that access and use a shop vacuum to clean the burner area. 

I did remove the wood panel in front of the furnace and blow the area out, and managed to see a label with the number "35436", which makes me think the model it's probably a Dometic (Atwood) DFMD35.

---

I do have a lifetime warranty from the dealership, but I believe I'm supposed to have it inspected once a year within 30 days of the anniversary date, and that's coming up in ten days on Dec 23.  So now I'm not sure which to try scheduling first - inspection or furnace repair.

Also, the first shop I called said they're backed up for the next six weeks, and the second wanted me to bring the RV to them - and I don't own a tow vehicle.

Man, this is a stressful situation.  Maybe I bit off more than I can chew.

[odigity]

For the furnace:

I went to dometic.com used their Find a Dealer tool (https://www.dometic.com/en-us/outdoor/find-a-dealer) to search for the nearest service provider, which turned out to be Lone Star RV, about ten miles away from me.  When I called them and told them it's for a Keystone RV, they said they only do JayCo now and sent me away.

For the annual maintenance service:

I went to keystonerv.com and used their Find a Dealer tool (https://www.keystonerv.com/find-a-dealer) to search for the nearest service provider, which turned out to be ExploreUSA RV Supercenter, about ten miles away from me.  When I called them, they said they don't offer annual maintenance service for warranties.

 

This is like a nightmare.  I just want it to end now.  Does anyone want to buy a 2019 Outback 240URS?  I'll give you a good price...

[Kirk W]

45 minutes ago, odigity said:

I don't own a tow vehicle.

In that case the only suggestion that I have is to contact a mobile RV repair service.

[odigity]

Finally found an RV repair shop with great customer service that was willing to help - and they're mobile.  Got an appointment for Wednesday.  Hopefully things continue to improve from here.  Once it's repaired, I'll post the details of what it turned out to be.

[Kirk W]

1 hour ago, odigity said:

 Once it's repaired, I'll post the details of what it turned out to be.

We would appreciate that as it is how all of us learn.

[RV_]

Whoa! Watched your video - that was much worse than mine was. Kirk is right, get some help before it gets too cold to do without. I had one backfire a little but not like that. I would also make sure your Fire ajnd CO detectors are no older than five years old. You might want to get a Propane detector/alarm too just to be safe.

[TXiceman]

I would not operate that furnace unit it was removed, and bench tested for proper operation by a qualified shop.  As for the lifetime warranty, the dealer should have explained to you that the unit had to come back to their shop for an inspection and that you had to pay for certain fees. 

Your best bet may be to just forgo warranty repairs and pay to have a certified shop repair or replace the furnace.  I had an almost 2-year-old furnace replaced by Surburban a few years back when it was not firing correctly.  There was an issue with the location of the ignitor and flame sensor.

Ken

 

[odigity]

The mobile TV tech guy came by today.  He performed the annual inspection/maintenance required for my warranty, then checked out the furnace issue.  His believes there's supposed to be a cover with a baffle attached to the external vent - that's the hole that fire explodes out of in the video I linked earlier.  His conclusion is that's probably the cause of the ignition problem.

He said he'll try to find the part and come back to install it.  I'll update when that happens.

[Kirk W]

1 hour ago, odigity said:

His conclusion is that's probably the cause of the ignition problem.

Thank you for the update. Can you get a closeup picture of the vent and post it so we might be able to detect if there is something missing. 

[podwerkz]

With no vent cover you may have some flying or crawling critters that got in there and made a home...mud daubers, wasps, moths, spiders and their babies, etc. These critters are often attracted to the smell of propane. 

It looks to me like a flame caused by the critters or debris flaming out...the backfiring seems to get less severe as the debris is burned up. 

Or so it seems to me. Yeah, there is supposed to be a cover and it's also a good idea to buy an aftermarket 'mud dauber' screen and install it. 

 

 

Edited December 15, 2021 by podwerkz

[Ray,IN]

4 hours ago, podwerkz said:

With no vent cover you may have some flying or crawling critters that got in there and made a home...mud daubers, wasps, moths, spiders and their babies, etc. These critters are often attracted to the smell of propane. 

It looks to me like a flame caused by the critters or debris flaming out...the backfiring seems to get less severe as the debris is burned up. 

Or so it seems to me. Yeah, there is supposed to be a cover and it's also a good idea to buy an aftermarket 'mud dauber' screen and install it. 

 

 

There is a valid reason the mfgr. states the warranty is voided if those bug screens are used. Reread the 1st page and RV's replies.

Edited December 16, 2021 by Ray,IN

[podwerkz]

41 minutes ago, Ray,IN said:

There is a valid reason the mfgr. states the warranty is voided if those bug screens are used. Reread the 1st page and RV's replies.

My reply was directed at odigity...and RV warranties are almost worthless...the lawyer lingo with all the escape clauses proves that. In most cases, for most of us, in most situations, if the day ends in 'Y' your warranty is void...if you even have a warranty. 

I just fix stuff and move on. Hold my beer while I have installed bug screens on all my RV furnaces since 1996.

 

[Wrknrvr]

New style Dometic/Atwood furnaces need a restriction in the exhaust for the system to function properly. There is a restriction device in the exhaust of this style furnace. That the factory installed when it was built.

  If this piece is removed the the flame in the burn chamber has trouble to stay burning.

  Back several years ago I had a hard time finding this out the hard way. So I finally called Dometic as a dealer. Was informed of how this system works.

  I have retired from rv repair. So I am not on the info on new stuff.

 Last summer I had a friend bring me a Dometic/ Atwood furnace to test. It was the power board.  But it did not want to stay burning Fter I installed a new power board, It would ignite, burn ,flame would go out, ignite again, burn, go out and just keep repeating this symptom.

  I quickly remembered the restriction situation. But I did not have that piece. So I put piece of steel in the exhaust to simulate the restriction as that part was at the friends place. He only brought me the furnace.

  And then the furnace worked as designed.

 

   Vern

[odigity]

12 hours ago, Wrknrvr said:

New style Dometic/Atwood furnaces need a restriction in the exhaust for the system to function properly. There is a restriction device in the exhaust of this style furnace.

...

  And then the furnace worked as designed.

Thanks for the confirmation - that makes me more optimistic that the tech is on the right track.

[RV_]

I installed a screen that kept bugs out still, yet stopped the backfiring. I called HitchHiker and RV there (No relation 😉) told me the screen, even though it was one of the large looking stainless steel store bought screens, was the problem. It worked in that situation. I only recommended to take the screen off to the OP and see if that solved it, as that cost zero, and is an easy check and suggests a solution as I outlined above with a slightly larger screen as I fabbed for mine. Quick rule out troubleshooting check.

I never suggested not having screens at all, just making sure you have everything flowing right with screens that work on each rig.. Today they make full sets - https://www.amazon.com/Protects-Furnaces-Insects-Stainless-Installation/dp/B07ZNG6QMG/ref=asc_df_B07ZNG6QMG?tag=bingshoppinga-20&linkCode=df0&hvadid=80470599116820&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584070152794676&psc=1

I also used the same material to screen the fridge side and roof vents, and sewer tank roof vent as well as the water heater opening. I used thin safety wire to secure them invisibly. I even screened the square old style rear bumper rubber cap vents as we had dirt daubers, wasps, etc. getting in all of them.

Yellow jackets still got in the water heater squeezing around that spring latch. Some today have a backer plate that does not allow them in there like in the picture below. My old one had the whole keyhole shaped latch hole open and they got in after I screened  the vent area shown with the better aluminum screen in my earlier post. I had two screws that fit them just right to be easy to put on when we parked for more than a day.

Safe travels! (without exploding furnaces)

Edited December 17, 2021 by RV_

[Kirk W]

On 11/28/2021 at 10:22 AM, Derek said:

Ours is outside vent port only, the furnace is nestled snuggly under the fridge

Just wondering if you have resolved your problems? Could you update us, please?

odigity, let us know what happens with yours also, if you will. 

Edited December 18, 2021 by Kirk W

[odigity]

On 12/15/2021 at 1:35 PM, Kirk W said:

Thank you for the update. Can you get a closeup picture of the vent and post it so we might be able to detect if there is something missing. 

The uncovered exhaust vent.

[Kirk W]

There is definitely something missing. 

                    

I start by replacing the outlet with a complete one. 

[odigity]

On 12/18/2021 at 9:45 PM, Kirk W said:

There is definitely something missing. 

                    

I start by replacing the outlet with a complete one. 

Damn - I somehow failed to notice your response.  Could have saved me some money vs having a professional do it. 

Luckily the professional did get it done, and now my furnace is working for the first time.  Photo attached.

[Kirk W]

Great news. Thanks for letting us know.