Atwood Furnace 8500-IV won't stay lit...

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redbug2

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Here are the facts: 2002 Citation 27foot travel trailer.

If I turn the furnace on the blower starts, standing outside near the exhaust I hear the igniter flashing, hot air comes out of the exhaust for a moment, then stops. Blower is continuous. The furnace cycles the igniter three times and three times it gets hot but won't stay lit.

Removed tanks and they have propane, stove works, gas fridge works.

I have noticed that the regulator (its an automatic changeover) shows the red indicator. Manual says it should be green... this may be the problem...

So, based on previous posts on this subject I am going to 1) Fill up the tanks to be sure they are not the issue and 2) Purchase a new regulator.

Any other ideas?
 
Usually this is a control board problem.  The flame lights up, but for the ignition to stop, it has to "prove" that the flame is steady and doesn't need the ignition input.  If it can't do that, there is a solenoid controlled valve that closes.  This is a safety control.
My Atwood is doing the exact same thing, but I have enough on my plate at the moment, so I haven't looked at it yet.

Another is that perhaps the ignition is making a poor ground.  This happens when the furnace is not used for an extended period of time.  This is from the igniter itself to a point near the gas tube.
 
We have a furnace trouble shooting document in the forum library - I wrote it so I know its good!  ::)  Check it out...

http://www.rvforum.net/index.php?option=com_content&task=view&id=333&Itemid=41

I don't think it is the control board  if the igniter works and the fan is running.  It may be that the flame sensor is not detecting the flame, as Nate says. That is usually the sensor itself or a bad connection in the wiring to it. Clean those connections to be sure - a pencil eraser is a good tool for cleaning contacts. The furnace should run for about 15 seconds if it is the safety shutoff that is stopping it.

It may also be an inadequate propane flow, based on your observation of the red flag in the crossover valve. The furnace needs a much higher rate of propane flow than your fridge or stove, so it can fail when they still run.  You could have some oily gunk in the regulator or a low point in the gas lines, restricting the flow.  You might try the water heater on propane to see if it works ok - it's another high flow appliance.

 
Thanks for the advice. Natetheskate called it right.

Took both tanks off and brought them to the local propane company. One was down 10 lbs, the other only 5. Filled them up anyway.

Visited camper store where I purchased the trailer used. Very nice people. I brought in the regulator but man at desk felt that was not it. Discussed the tests that I had done (Stove works, Fridge works, etc.) Man called his mechanic out front, I described the case to him. Without hesitation he said "Computer Board". They also wanted me to light all three burners first and see if there was any drop in the first burners flow as the others were lit. Purchased new board $140 ouch, just in case. They re-sealed the computer board  box and were willing to take it back if the stove test failed.

Got home, tanks back on, regulator back on. Turned on stove burners, 1,2,3 no decrease in flame.

Put new Computer board in, one set of clicks on start up and there was no looking back, there was heat!

Talked to my neighbor who has an airstream, he said this is common problem. He said sometimes he brushes the board contacts with a pencil eraser and gets it to work again... I will try doing the eraser later, but for now, I will use the best, and save the rest.

Regards,  :)

Will
Pottstown, PA

Thanks again.
 
Furnace boards are pretty simple and  rarely fail, but the contacts get corroded, especially the ones for the flame sensor. A clean-up would likely do the trick.  I suspect that replacing the board, i.e. reseating all wire connections, effectively did that. But now you have a spare board, just in case.  ;)
 
The flame sensor is connected to. . . the control board!  And while they are pretty simple, they can go bad, and just because other functions work, doesn't mean some other part is OK. 

There is a place called www.flightsystems.com that can check the board for a fee of $35 (never used them, but they advertise) AND they sometimes look for "cores" that perhaps you can get some of the money back.
 
Flame sensor:

I had the same exact problem years ago.  Finally someone to me to replace the flame sensor and that cured the problem.  By that time could remove the furnace in 5 minutes.  Quite a few  years ago but as I recall the flame sensor was just a bare wire above the flame.  It cost around $35.

The flame sensor is sort of like a thermcouple.    The flame sensor must detect the presents of a flame in just a few second after iginition.  If there is no flame detected the gas valve shuts off the gas for obvious reasons.

Cool system while everything works. ;)

Jim
 
Used the trailer for the first time in over two years at the Punkin Chunkin near Dover De. A good time to test my new board. Second time I used the trailer, first time in the cold... Heat started fine but then shut down in the middle of the night. I shut the furnace off, waited a few minutes, then turned it on... Worked fine for the rest of the weekend without any problems.

Had some issues with hot water heater, user error... I had turned off the switch on the outside when winterizing 2 years ago, its kind of hidden behind the gas parts, forgot about it,  and also had my bypass valve open..  Finally figured that out....

Got it home at 2 in the afternoon and re-winterized with RV anti-freeze.

Good to get it out and use it... Found one other problem, will list in another thread.
 
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