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Furnace Ignites Then Quits

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I have a 2006 Fleetwood Pace Arrow with an Atwood furnace model 8531-IV. Until today it worked fine. Now it ignites but quits after a few seconds and cycles through 3 times. I notice then a red flashing LED on the motherboard after the cycle with 3 flashes then a pause before 3 more. The manual says the code indicates "ignition lockout fault". What can I do?

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Check the ignitor also, the air gap might be too large or the porcelain on the ignitor/thermister might be cracked...

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Gas furnaces use a flame rectification pilot proving system, the spark is AC initially, however as it passes through the flame, its rectified to a DC signal, via Flame rectification. A flame isn't a great conductor, but it allows millivolts/milliamps(not much, easily disrupted) of a DC signal to be sensed by a sensing rod, and /or ground via the pilots assembly etc.

There will be a ground, or sense terminal on the ignition module or board. The signal in DC returning on ground/sense is what proves a flame exists ,or the pilot and is safe to then transition to full burners-- this is a good thing, especially with propane.

There are centrifugal pressure or a sail switch that proves the induced draft motors running and says go to spark, but not always. Sometimes the pilot drops from the pressure, centrifugal or sail switch not proving a induced draft exists, especially if its a pressure switch.

The orifices where the tube attaches on the induced draft blower assembly, carbons up and requires a tiny drill bit to ream out the tough carbon plug/deposit, sometimes they are partially blocked causing a wavering and on/off as your as well. It can be several things without seeing it, impossible to tell definitively, but these are where to look and how.

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