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guidocat's avatar
guidocat
Explorer
Feb 03, 2015

Atwood furnace with intermittent lockout and NO ACCESS DOOR!

So we are fulltiming in a Keystone Impact 300 toyhauler and having a wonderful time. We have survived a lovely summer and a few weeks well below 0.

A day or two ago we started waking up to freezing cold and finding that we had to power cycle the thermostat to get the furnace to run. Eventually, the furnace developed a habit of only starting maybe 1 out of 3 attempts.

When the furnace would fail it would do this specifically. The thermostat would ask the furnace to start making heat. The blower turns on and there is NO click of the igniter. The blower shuts off after 15-20 seconds and goes into lockout. Cycling the power allows it to try this again.

Once the furnace ignites it will run for hours if the temperature is set to 100 without missing a beat.

By the way, it is super cold outside, and it seems to get a little better as it warms up outside.

So, any ideas? And if the suggestion is to look at/probe/test a thing, how the heck am i supposed to get to it without an access panel!?!?

11 Replies

  • guidocat's avatar
    guidocat
    Explorer
    Feb 05, 2015
    Well it looks like I'll be ripping this nonsense out so I can at least look at it.

    Does anyone have any experience removing one of these boxes. The service manual claims 0.3 hours for removal, so they must have made it reasonably easy to get out.

    If anyone can point me to a tutorial, or at least give me some clue what I'm getting into, I would appreciate it.

    Love,

    Ron
  • joebedford's avatar
    joebedford
    Nomad III
    Feb 04, 2015
    I had the exact problem you are having and I discovered the cause by pulling off the outside panel and wiggling the wires while the furnace was attempting to light. Turns out that one of the ignitor push on spade connector was loose causing an intermittent start. I pinched the female plug with pliers and reinstalled. Voila - problem solved.

    BTW, the control board in the furnace (visible from outside) has a LED that flashes a failure code that you can try to interpret.

    Finally, propane doesn't vaporize well in extreme cold - make sure your tanks are full.
  • guidocat's avatar
    guidocat
    Explorer
    Feb 03, 2015
    Doug,

    From my understanding those are the only two options for why i'm not hearing an ignite cycle, other than a blown control board. So you think those things may fail on a 6 month old furnace? Granted, one that has been lived in full time in New England all winter.

    So, enblethen, there are punch outs in the front that are pretty big, 3-4 inch diameter. What do you fellas think about punching one out to access the possibly failed components, and then taping them back up?

    Any promise there?

    I really dont know where the sail/overtemp switches are, or whether they would be accessible from that angle. What do you think?

    Again, thanks for all the insight gang.
  • enblethen's avatar
    enblethen
    Nomad
    Feb 03, 2015
    If you can get to the top of the furnace there should be some ventilation holes. You could try using some compressed air to blow dust out. Air compressor with nozzle or even a can of computer air.
    That may be all it needs.
  • dougrainer's avatar
    dougrainer
    Nomad
    Feb 03, 2015
    There is NO way to work on your model without pulling the complete furnace. I would be inclined to suspect the hi limit switch rather than the sail switch. Hi limits(Atwood) are common (for service people when under warranty) to fail. They "stick". If you suspect your sail switch, a quick way to test is when it fails to light, gain access to the inside furnace casing and bang on it. If the sail switch is sticking(very rare) this may free it up. Of course banging on it may unstick the hi limit also. If you are going to do the work yourself, then replace both the sail and hi limit switch. Doug
  • guidocat's avatar
    guidocat
    Explorer
    Feb 03, 2015
    The atwood website has a single 7 page manual...not exactly a technical guide...anyone know a place to get a real manual?
  • midnightsadie's avatar
    midnightsadie
    Explorer II
    Feb 03, 2015
    go get a couple electric heaters till it warms enough to work on it, the manual is your best short cut.
  • guidocat's avatar
    guidocat
    Explorer
    Feb 03, 2015
    Yeah, that is one of the most depressing documents I have ever read. It says to remove the entire unit for service. I'm hoping to find a shortcut, because that sounds like a bad night to me.

    Someone tell me there is a shortcut.
  • enblethen's avatar
    enblethen
    Nomad
    Feb 03, 2015
    Lost of air flow during heating function would cease when the sail switch contacts open and then the blower would still run in the cool down mode and shut off.
    Go to the Atwood website and download manual for your furnace. It will tell you how to install it. This should give you some idea how to service it from inside the rig.
    Atwood
  • guidocat's avatar
    guidocat
    Explorer
    Feb 03, 2015
    Thanks for the quick reply.

    I'm running on shore power. And I'm definitely under the impression that I'm getting less airflow than I did initially.

    Now, how I understand it, if the sail ever fails to register air flow the furnace will shut off. Wouldn't you expect that sometimes the furnace would shut off mid cycle if that were the issue?

    The model is 8520 IV.

    Thanks for any help you can offer.

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