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Post by termy251 on Feb 6, 2023 14:20:41 GMT -5
Any Furnace experts out there?
Ok, first this is not on a KZ Product, Sorry, not my camper but really scratching my head trying to fix this. ATwood 8500 series Furnace, The gas ignites but will not stay on. Sail Switch working, Hi Low sensor working, Burner pulled and cleaned, No cracks in the screening on the burner, igniter sparking and working. Gas works on stove and hot water heater. Tried different propane tank just in-case low pressure issue. So here is what happens -
Turn on heater, runs for about 15 secs to purge the gas in the burner tube. The gas valve opens up and the igniter sparks, I can hear the gas ignite and feel the heat from the exhaust tube, but flame goes out. The sequence for the lighting runs 3 times before it times out with an error and does not light. Any ideas of more trouble shooting? I have exhausted my knowledge on what to check next.
I have watched about 50 different you-tube videos but cannot figure out how to get this thing working.  What do you guys think? Thanks, Kerry This is on a 2007 Monaco 5th wheel camper that belongs to a friend of mine.
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Mark T
Newbie RV’er
Longer days ahead.
Posts: 43
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Post by Mark T on Feb 6, 2023 16:21:31 GMT -5
Depending on model, there may be an LED on the control board that will indicated the fault. Check the manual on this.
It could be the over temp limit switch not made if the wire is loose or fell off. From an Atwood manual (might not be your unit) it looks to me like the over temp would have 12V going through it and it would be normally closed because the 12V coming out of it goes to the control board and also to the sail switch. So I would see if the over temp out/sail in has 12V.
There is also a wire that comes from the gas valve to the control board. This is likely the flame sensor input to the control board. I would guess this should send 12V to the control board when flame is sensed, but it may be the other way. Would be nice if they included the theory/sequence of operation in their manuals.
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Post by nvguy on Feb 6, 2023 23:36:53 GMT -5
Yes, it doesn't seem to be sensing the flame, I would have to see the manual to refresh my memory, but typically the ignitor also serves as the flame sense (the flame creates a path to ground) so the location of the ignitor within the flame is critical. Also, the general condition of the ignitor, any cracks or damage to the insulator can cause issues.
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Post by termy251 on Feb 7, 2023 8:34:44 GMT -5
Thanks for the information, I ordered yesterday the igniter and burner to see if that helps when it comes in. When I removed it, It does spark to ignite and the gas does ignite but it does not stay lite.
So i was thinking it was some kind of flame sensor or something. Makes sense if the igniter is also controls the flame sensor since I do not see anything else in that area of the burner.
Everything I was researching said the sail switch and the HI-Low switch should be good since the Gas and the igniter are sparking. The 12v will not spark if those 2 switches are bad.
It shows Atwood 8940-III DCLP but I believe it is the same as all the Atwood 8500 series furnace. They look the same and I cannot find anything on the 8940 series units.
I will let you know what happens after the parts come in.
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Mark T
Newbie RV’er
Longer days ahead.
Posts: 43
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Post by Mark T on Feb 7, 2023 20:47:24 GMT -5
According to the 8940 manual here - search on manualshelf.com for "Atwood 8940", there is an LED in the furnace that will indicate fault codes: ![]()  |
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Post by termy251 on Feb 8, 2023 7:53:40 GMT -5
Yes, The fault code was ignition lockout. Just means it did not light. haha, I did find something though, have to test it tonight.
The exhaust tube should have a piece in it for a little back pressure, That is why the system will not run if you do not have that tube in.
Well, Stupid me, I was wondering why the tube was bent up so I straightened it out. I will re-bend the tube today when I get home from work to see if that works.
I will let you guys know how it goes. Once again, thanks for all the information anybody has. well appreciated.
Kerry
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Post by termy251 on Feb 14, 2023 10:39:33 GMT -5
Just wanted to update. i found the problem, mud dobbers built a nest in the gas line. since the line was open because the person I bought it from had an external propane tank, the line was open. The furnace is a lot more touchy on the pressure than the hot water heater and the stove. Because they were working i thought it was good. All cleaned out and good to go.
Thanks for any suggestions.
Kerry
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