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Topic: Atwood Excalibur III 8535 heater poor combustion (Read 989 times) previous topic - next topic

Atwood Excalibur III 8535 heater poor combustion

The single propane furnace is my 1998 U270 is not working properly. It stinks of combustion gases (not a leaking propane smell) and has black soot on the exhaust tube visible both inside and outside. I pulled the outside cover and did not see any obvious obstruction in the tube or squirrel cage fan that draws in combustion air. I pulled the inside vent cover but couldn't see anything of note. I've used it a lot since November, but for two weeks had good 50 amp power and used the rooftop heat strips. Was mooch docking with 15 amp power, went back to the Atwood furnace and the next morning it was stinking up the driveway. CO detector, which is new, did not go off. My local RV tech is booked up through the month and everybody in the county is having furnace problems. Moved to new site with good 50 amp power, running coach on electric but it is really getting cold over the next 10 days here in North Texas.

Suggestions welcome for how to proceed.
1998 36 foot U270 Build No. 5328 WTFE, 900 watts solar, Victron controller, B2B, bat monitor, 600 AMPH lithium with 2018 Chevy Colorado toad, SKP #110239, Motorcade #17781, 2021 Escape 17B for when Coach is broken down and campsites are too small, retired and full-timer since Dec. 2020. Part of RV family since 1963.

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #1 –
It looks like your air mixture is off and you are generating a lot of soot.  If not, you may have a crack in the chamber as it could do the same thing.  You would get the smell of combustion, but it may not be enough to set off the C02 alarm.  Can you access the chamber and take a look at it?  Hope this helps!  Good luck!
Try pulling up Atwood help center and see what they say to look for.
Joe & Dottie Allen
Sold!  December 2023.      2000 U320; build # 5645
Our coach " Maxine"
Motorcade #  15922;  Escapee 150950; FMCA F330833; Boondockers Welcome;  Harvest Hosts;  Thousand Trails
'98 U320 from 2000-'06
USAF '62-'66

"Do not spoil what you have by desiring what you have not; remember that what you now have was once among the things you only hoped for." ―Epicurus

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #2 –
I had a furnace in another motorhome that was doing that. I pulled out the exhaust tube that looked like yours and cleaned it up with solvent. Sometimes mud dobbers can get in there also.. It doesn't take much restriction to cause problems. The tube is usually just held with a single bolt behind the outside cover.
Good luck with it

Larry
Larry & Debbie Town
2000 U320 4210 
Previous 88 GV

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #3 –
You might have a dirt/mud dauber nest that is in the combustion chamber tube as it looks like you don't have a bug screen.  Take a wire cloths hanger and straighten it out.  Use this to gently probe in the exhaust side to see if you can fish something out. If nothing then joe is on the other track.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #4 –
I concur with Joe , had the same issues with mine, pulled it out took it completely apart and found cracks in the chamber, had it tig welded put it all back together and it worked for a short time but could still smell it, so I replaced it with a OEM.
Andy & Eileen
MONTROSE COLORADO
1992 U300  40' 6V92 TA
2016 4 Runner
1998 Jeep Grand cherokee

1998 Jeep Grand Cherokee) Build # 4135 Skp# 122921

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #5 –
See if the trouble shooting section is of any help?

RV Products 8535 SERIES Service manual | Manualzz
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #6 –
Looks like you may need to rebuild the burner and igniter area,couple of places sell kits to do this,think if the exchanger had the crack it would not be causing the soot,while your in there get a new fan motor,yours will be screeching soon.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #7 –
The burner assembly is no longer made and out of stock in all the usual places. Not good. If I tear into this and the burner is bad I will have to find a replacement. The domestic somewhat equivalent also appears to be on back order. This could turn into a a major retrofit project.
1998 36 foot U270 Build No. 5328 WTFE, 900 watts solar, Victron controller, B2B, bat monitor, 600 AMPH lithium with 2018 Chevy Colorado toad, SKP #110239, Motorcade #17781, 2021 Escape 17B for when Coach is broken down and campsites are too small, retired and full-timer since Dec. 2020. Part of RV family since 1963.

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #8 –
Quote from: Realmccoy –
The burner assembly is no longer made and out of stock in all the usual places.
Patrick,

What part number are you looking for and finding out of stock?  If it is "Burner 32811" then I might be able to help.

See Reply #6 in the thread linked below:

Need Hydro Flame Furnace Burner

I installed the burner I got from Amazon 7 years ago and it is still working perfectly (AFAIK).  In fact, it has been cycling on and off all day today cuz it is 19 degrees here.  Tomorrow it will supposedly hit a low of -3 degrees F    :o  so I'm sure hoping both our heaters continue to function.

Amazon.com: Atwood 36043 Burner: Automotive


As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #9 –
I am looking for that elusive 32811! I'm currently hiding out in Galveston from the -2° forecast in North Texas. When it warms up I'm going to tear into the furnace and if it is the burner then I'm going to replace the burner, fan motor, and control board.
So long as heat exchanger looks okay.

The reviews on the newer furnaces are not very encouraging.

Thanks for responding.
1998 36 foot U270 Build No. 5328 WTFE, 900 watts solar, Victron controller, B2B, bat monitor, 600 AMPH lithium with 2018 Chevy Colorado toad, SKP #110239, Motorcade #17781, 2021 Escape 17B for when Coach is broken down and campsites are too small, retired and full-timer since Dec. 2020. Part of RV family since 1963.

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #10 –
Please double check for carbon monoxide from the heater.  Make sure all detectors are working properly!  Please post your findings as well.  Stay safe!
Joe & Dottie Allen
Sold!  December 2023.      2000 U320; build # 5645
Our coach " Maxine"
Motorcade #  15922;  Escapee 150950; FMCA F330833; Boondockers Welcome;  Harvest Hosts;  Thousand Trails
'98 U320 from 2000-'06
USAF '62-'66

"Do not spoil what you have by desiring what you have not; remember that what you now have was once among the things you only hoped for." ―Epicurus

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #11 –
While you have it all torn apart, check the condition of the spark and temp sense electrodes.  Clean (if necessary) and adjust gap to 1/8".

See page 25 in the manual I linked above (Reply #5)
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #12 –
Just a FYI, if you hit a dead end on parts try this guy, Tristate RV parts. 517-448-4433.
I got a OEM new in the box for around 600 bucks shipped.
Andy & Eileen
MONTROSE COLORADO
1992 U300  40' 6V92 TA
2016 4 Runner
1998 Jeep Grand cherokee

1998 Jeep Grand Cherokee) Build # 4135 Skp# 122921

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #13 –
I'll check them out. Thanks for the suggestion. Their website is down at the moment.
1998 36 foot U270 Build No. 5328 WTFE, 900 watts solar, Victron controller, B2B, bat monitor, 600 AMPH lithium with 2018 Chevy Colorado toad, SKP #110239, Motorcade #17781, 2021 Escape 17B for when Coach is broken down and campsites are too small, retired and full-timer since Dec. 2020. Part of RV family since 1963.

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #14 –
Thanks for heads up Joe.

When it comes to Carbon Monoxide, we have redundant detectors in the bedroom and some other locations.

They are inexpensive battery operated with digital displays.

Much more fun to not wake up dead from our CO or a from a neighbor's CO.

Seems to happen too often and is fully preventive-able.
 

Re: Atwood Excalibur III 8535 heater poor combustion

Reply #15 –
Update: warmed up enough to mess with furnace. Flu pipe was the happy home of mud dobbers. Removed it, cleaned it out and furnace is better. Also learned that my paperwork on the furnace was inaccurate. My data plate says Atwood 8940 iii dclp. Will dive into it further when back to some place I can receive parts. I'm going to pull burner and motor for deeper assessment when a bit more settled. I suppose this falls into the category of owner neglect/ignorance.
1998 36 foot U270 Build No. 5328 WTFE, 900 watts solar, Victron controller, B2B, bat monitor, 600 AMPH lithium with 2018 Chevy Colorado toad, SKP #110239, Motorcade #17781, 2021 Escape 17B for when Coach is broken down and campsites are too small, retired and full-timer since Dec. 2020. Part of RV family since 1963.