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Old 09-19-2010, 12:12 PM   #1
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Furnace come on and shut right back off

I have 2007 3400RL I just tired to turn on the furnace for the first time this year, the fan come on and then it will lite,but will only stay on a couple of seconds, then off it will do this 3 times and then shut down. I took the cover off on the out side and saw the lite on the circuit board it flash 3 time,the book said the 3 flashes was Ignition Lockout Fault. Has any one else had the same problem.
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Old 09-19-2010, 12:21 PM   #2
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Something to check. It almost sounds like the problem some of us have been experiencing with our propane pressure. One way to check is light a burner on your stove when you start your furnace. If the furnace continues to act up and the burner is OK then it may be a plugged oriface on your furnace. If your stove flame goes down or out you may be experiencing the same regulator problems others have been talking about. Just a thought.

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Old 09-19-2010, 01:20 PM   #3
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Your furnace has an air flow switch in it. If it doesn't trip with the blower on, the gas valve will not turn on. The switch can get dirty or an insect or mouse could have stuffed stuff in there.

The sequence for the furnace is... blower on, air flow sensed for a short time, gas valve on, sparker ignites gas, flame detected, runs till thermostat is satisfied, gas valve shuts off, blower runs for short time, shuts off.

If air flow or flame are not detected, the system shuts down before the thermostat is satisfied.
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Old 09-19-2010, 02:30 PM   #4
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Thanks when my unit come on the fan start and runs a few seconds then the furnace lites and only satys on a few seconds heat does come out during those few seconds,so I no it lites but just won't stay lit.
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Old 09-19-2010, 02:56 PM   #5
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Is it actually lighting or are you hearing the click, click, click of the ignitor trying to light the gas?

We had a 2006 3400 where we detailed our experiences and fix for the problem:


There are just a few basic parts to these blasted furnaces.

First, there is the circuit board, which is the easiest to replace. Typically, if the fan is blowing and WON'T turn off unless you either pull the 12v fuse or turn off the unit on top (there is a switch), then it is probably the circuit board.

Second, there is a sail switch. This is a switch inside the fan housing (4 screws to get the fan housing front half off). This switch has a long piece of metal on it about 1/4" wide. As the fan turns, the air pushes against this long thin metal strip and pushes it closed, which activates the switch. The switch is now allowing 12v to go thru it which in turn allows the gas valve to be able to operate.

Third is the electrode. This is a bear to replace (I did it, and it took me an hour to get the old one out and the new one in by wiggling it every which way in a very cramped space). The electrode, if bad, won't "spark" and ignite the gas. If you go to the trouble of getting the unit all the way out and on a bench, then I would take the extra time and replace the electrode.

Fourth is the gas valve. I haven't replaced this valve, and if it ever gets to that point, I'm just going to order a new furnace. Looks too complicated and dangerous, at least to me.

So, in order of price, it goes 1, 4, 3, 2. Roughly $170 for the board and just a few bucks for the sail switch and electrode. Don't know the price of the gas valve.

In order of difficulty, it goes 1, 2, 3, 4.

In order of your problem, I would suggest #3. Let me ask you: Does you furnace ever light? The unit will try 3 times, then "lock out", so you have to turn the unit switch off then back on. When you turn it back on (with the t-stat turned to furnace and calling for heat - set to 99 degrees), the fan should come on, then the ignitor on the circuit board (after about 20 seconds) should go click, click, click and then the propane should be burning. If the propane does not ignite, the exhaust sound will not change, and then the board will try a second and a third time.

Oh, I would try one thing first. Open your stove hood and disconnect the gas to the burners. Fit a gas guage on to the propane supply line. It should read between 10 and 14 inches WC or about 3 lbs of pressure. But, Atwood's manual states that before doing a pressure check, to first disconnect the propane supply and cap this supply line to the furnace. If the pressure is low, go to your regulator and adjust as necessary (under the black cap on the regulator).

Sorry for the long post, and hope that what I wrote makes sense to you. Good Luck!
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Old 09-19-2010, 03:10 PM   #6
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Yes it is lighting.
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Old 09-19-2010, 03:14 PM   #7
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Check out this website. http://www.ehow.com/how-does_4827001...v-furnace.html
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Old 09-20-2010, 12:20 PM   #8
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i had this problem with mine .camper4 said it right. there is a switch on the blower that the blower has to reach a certain rpm before the furnace will run. that switch needs cleaning .i tore my furnace all out and took it to a tec.watched him clean it then tried a dozen times and works great .all he need was clean and check it .works great now and he charged my nothing .it was a good rv dealer.
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Old 09-21-2010, 03:06 PM   #9
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Propane pressure was mentioned and is a possibility. Fan speed was mentioned and also is a possibility. One thing often overlooked is whether the battery can maintain sufficient voltage to the board. Even though you may be plugged into shore power the board still draws 12v from the battery. Just something more to check.

Also, we've had problems at times with spiders building webs in the gas tube behind the outside furnace cover and that can restrict the gas flow.

If you replace the board, I'd highly recommend you buy the Dinosaur brand board rather than replace with the same as the original. I am not sure the price but think they're very comparable in price. The Dinosaur is a much more reliable and longer lasting board.

Another time we had a problem very similar to yours. This may not even be close to your problem, though. In our case, it was actually the fan that shut down. That caused the (can't remember its name) valve to close which shut off the gas flow. It turned out to be a bad connection to a switch on the fan housing. You might try just wiggling the wires and see what happens. That's how I found out the problem with ours. That was about 3 years ago and we've had no further problems.

Good luck with yours. This kind of problem can be very frustrating, at least to me.
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Old 09-23-2010, 02:40 PM   #10
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Have this happen perodically around the first of the heating year. after the 3 failed attempts I turn the furnace off at the T'Stat, wait a couple of minutes and turn it back on. The turn off resets everything, normally starts the second time around and no further problems. Have had this for years with this and other RV's, nature of the beast.
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Old 09-24-2010, 04:42 AM   #11
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I had this same problem on an sob. A wasp had made a nest in the exhaust tube of the furnace. I now put screens over them. Good luck.
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