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Author Topic: Atwood 8900-Iii furnace problem  (Read 314 times)

Capt Tom

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Atwood 8900-Iii furnace problem
« on: November 24, 2017, 02:53:31 PM »
My 2005 5th wheel furnace hasn't been used for several months. When I turned it on it made a weird screaming noise, after opening the outside cover and taping on things, the fan will come on, then will light and burn for about 10 seconds, the fan remains on, after about 10-15 seconds it will relight and do the same thing. It does the customary three tries, then shuts down. The red light on the board will flash. Then you have to reset and start all over, does this each time. Any help would be appreciated.

Gary RV_Wizard

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Re: Atwood 8900-Iii furnace problem
« Reply #1 on: November 24, 2017, 05:10:19 PM »
Try my article on Furnace Troubleshooting in the forum library at http://www.rvforum.net/miscfiles/Furnace_Trouble-2.pdf
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Capt Tom

  • Posts: 2
Re: Atwood 8900-Iii furnace problem
« Reply #2 on: November 25, 2017, 10:24:58 AM »
Gary, I looked over the suggested page, could find nothing sim alert to my problem. The furnace ignites but won't stay on but several seconds, it will do this three times then lock out. Is this a connection problem?  I read that the unit has a sensor to determine that the flame is correct, if this is the problem, where would I find this connection?

Alfa38User

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Re: Atwood 8900-Iii furnace problem
« Reply #3 on: November 25, 2017, 10:33:32 AM »
The dual purpose flame detector and igniter lies directly in the flame. Simply follow the wire to the connection on the board, remove it, clean both the wire connector and the board connection well and reconnect. (The detector generates a very small voltage when heated by the flame and a dirty connection will often prevent its proper functioning.)
« Last Edit: November 25, 2017, 10:36:25 AM by Alfa38User »
Stu
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Gary RV_Wizard

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Re: Atwood 8900-Iii furnace problem
« Reply #4 on: November 26, 2017, 12:26:43 PM »
Quote
Gary, I looked over the suggested page, could find nothing sim alert to my problem.

I guess my guide is more of an information source to reason out the problem than a simple symptom & solution booklet.

As Alfa38 explained, the igniter is also the flame sensor, so if it ignites then it can also sense. However, the sensor sends a very low voltage signal back to the controller board and it is easily lost to a bit of corrosion. Of course, it is also possible that the igniter has gone bad in a way that affects only the sensing function. That's relatively rare, but not unheard of.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

Senator

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Re: Atwood 8900-Iii furnace problem
« Reply #5 on: December 15, 2017, 05:20:53 PM »
I know nothing about RV furnaces, but fix a lot of residential furnaces.  It sounds like a flame sensor.

Even if the igniter and sensor are the same part, the sensor has to have a different voltage or something different than the igniter.  Otherwise, there would be no need for a flame sensor once the ignition cycle started.

You can clean it with steel wool, or even a dollar bill.  Or replace it.  A residential flame sensor is about $10-$15.

Gary RV_Wizard

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Re: Atwood 8900-Iii furnace problem
« Reply #6 on: December 16, 2017, 09:44:03 AM »
Yeah, the igniter works by receiving a high voltage pulse from the control board to jump a spark from the electrode to nearby metal (ground). The sensor in the same component generates a very low voltage & current when heated by the gas flame and that signal travels back down the same wire that provides the high voltage pulse. The controller is watching for that sense voltage at all times after it opens the gas valve and attempts ignition. If the sensor voltage is not detected, it closes  the gas valve again. A common problem is corrosion on the end of that wire that prevents the low voltage signal from being detected.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

 

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