Atwood On Off

[joraz]

My 95 coach has the original Atwood heaters. Both have been working well. Today, my front one started behaving strangely. When the thermostat called for heat, the fan would start as usual and the burner would ignite as usual. However, after burning for maybe three seconds, the burner would turn off (the fan would keep running). Anyhow, I cycled it maybe five times or so and now it's working perfectly. I was thinking the limiter switch or the circuit board but was surprised when it began working again. Ideas? Thanks.
jor

Arghhh... just cycled on again and no fire. Darn!

[Jagtech]

wa8yxm wrote:

Jagtech wrote:
Possibly the sail switch is starting to fail; it can be intermittent for a while before failing completely.

NO, not possible, if it was the sail switch it would not light at all.

Wrong... on mine, the sail switch (micro switch) was "flakey", would contact for a few seconds, then open. The furnace would fire, then fail. A new switch fixed it.

[Old-Biscuit]

Filling propane tank with 'bleeder' valve cracked open is the proper way to add propane to your MH tank.
Liquid will spew out when 80% level is reached.

[joraz]

I'd bet it was air in the propane line.

Well, I'm thinking that you're correctomundo! Both furnaces are now working as before. In the past I've had this issue with the range and oven but never with the furnaces. Anyhow, thanks to everybody else for the troubleshooting tip. I'm printing them and saving for future issues.
jor

[John_Wayne]

If this happened and you haven't used the furnace for while (weeks ) I'd bet it was air in the propane line.
Mine will do the same thing it will try and light and I can hear the flame for a few seconds. I will do it 3 times and then just the fan will run.Have to turn the thermostat off and on again to restart 3 tries. Have to keep doing this till the air is out of the lines.

[joraz]

Thanks to all for your advice. I'm going to troubleshoot this today. We're in Oregon and of course, it't raining (hate rain as I grew up in Seattle!).

Just now, something else occurred which may point me in another direction. The back furnace, which has been on all morning, started blowing cold. It lighted again but it's never done that.

I put a new regulator on my propane tank a few months ago and everything has been operating fine.

I also filled with propane (78 gal tank) a few days ago at a Flying J. The guy filling it used a method I had not seen. He hooked up the hose and turned on the pump. Then he opened and left open the safety valve. He left it open until propane spurted out, then turned off the pump. Is it possible that I have too much LP in the tank with not enough space above it? Just opened the safety a hair and get only vapor. Thanks.

Both furnaces were just working again. I'm thinking this has .got to be a bad regulator or some kind of fuel related issue. Frig is working on propane and range burners light .
jor

[wa8yxm]

Let me post the boilerplate.. Then you can track it.. I would guess the flame sensor the connecting wire or control board. Burner adjustment or a partially clogged burner are also possible but lower on the list. Try cleaning the flame sensor and since most of the labor is duplicated the burner orifice first.

When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps nby the way So does bad wire/connection.

[wa8yxm]

Jagtech wrote:
Possibly the sail switch is starting to fail; it can be intermittent for a while before failing completely.

NO, not possible, if it was the sail switch it would not light at all.

[Old-Biscuit]

Erratic Furnace main flame

Blocked or obstructed exhaust
Spark electrode/flame sensor out of position (should be directly over burner slot and engulfed by main flame)
Spark to ground gap should be 1/8"
Cracked ceramic can cause erratic operation...flame signal goes to ground instead of to circuit board
Dirty/loose contact on connector to circuit board
Flame sensor failing

[Jagtech]

joraz wrote:
Hmmm... can't get the quotes to work.
Thermo Coupler: Sounds promising. I'll check.
Sail Switch: Wouldn't that prevent it from lighting? It lights and goes out.

It's an Atwood 8516-III
Thanks.

I had a sail switch that was just starting to fail, and acted just like you describe. Easy test - put a (temporary) jumper wire across the sail switch contacts, and see if the unit functions properly.

[joraz]

Hmmm... can't get the quotes to work.
Thermo Coupler: Sounds promising. I'll check.
Sail Switch: Wouldn't that prevent it from lighting? It lights and goes out.

It's an Atwood 8516-III
Thanks.

[Jagtech]

Possibly the sail switch is starting to fail; it can be intermittent for a while before failing completely.

[Passin_Thru]

The thermo coupler that keeps it lit once it's lit can go bad (if it has one) It is a a Thermo (kept open by heat) switch and it looks like a tube smaller than a pencil sticking in the area where the burners flame would contact it. Make sense?