Furnace won't start - Humidity

[mtnhigh]

We have a 2017 fifth wheel. We love it. Have over 12000 miles on it in the two years we have had it. The furnace won’t start regularly on humid days.

1. Starting the furnace and ~15 second latter the spark gap fires. And then about 7 second later you can hear a value close. I believe this is the gas value closing. Then about 15 seconds later the spark gap fires again. No ignition. About 7 second later the value closes. Then again about 15 seconds later the spark gap fires again. No ignition. Then again about 7 seconds later the value closes. And about 15 seconds later the furnace fan turns off. If I reset the system and go through this process 3 or 4 times the furnace will sometimes start. But not always.
2. Once started the furnace will not keep running. I believe the temperature in the furnace reaches a high enough temperature that the controller shuts the flame off. Then some time later you can here the spark gap firing again. And it goes through the three cycles again but does not light. And the furnace will go off again.
3. I got back home to Denver where it was 80 degrees and very low humidity and the furnace starts right away on the first spark gap firing.

Does this sound like the sail switch? Since the controller fires the spark gap three times trying to start the furnace it seems more like it is the humidity that is causing the problem. We were in heavy rain at night and the humidity was very high. Any words of wisdom from those of you that might have had this problem?

[cpaharley2008]

In the past it has always been the sail switch which routinely would get clogged with debris. Humidity is a new one.

[Oldtimer]

We had the same thing happen to us on the way home from the Escape rally. Pulled and cleaned the sail switch same issue. Replaced sail switch still no go. Had the board replaced under warranty, furnace fires up perfectly now. Me thinks it’s your board that is bad

[mtnhigh]

Thanks for the information. After your feedback and the video that Escape put together for the replacement of the sail switch and igniter control board, i do think I need a new controller. I will look around to find one. Thanks

[suncoastdancers]

Originally Posted by mtnhigh

We have a 2017 fifth wheel. We love it. Have over 12000 miles on it in the two years we have had it. The furnace won’t start regularly on humid days.

1. Starting the furnace and ~15 second latter the spark gap fires. And then about 7 second later you can hear a value close. I believe this is the gas value closing. Then about 15 seconds later the spark gap fires again. No ignition. About 7 second later the value closes. Then again about 15 seconds later the spark gap fires again. No ignition. Then again about 7 seconds later the value closes. And about 15 seconds later the furnace fan turns off. If I reset the system and go through this process 3 or 4 times the furnace will sometimes start. But not always.
2. Once started the furnace will not keep running. I believe the temperature in the furnace reaches a high enough temperature that the controller shuts the flame off. Then some time later you can here the spark gap firing again. And it goes through the three cycles again but does not light. And the furnace will go off again.
3. I got back home to Denver where it was 80 degrees and very low humidity and the furnace starts right away on the first spark gap firing.

Does this sound like the sail switch? Since the controller fires the spark gap three times trying to start the furnace it seems more like it is the humidity that is causing the problem. We were in heavy rain at night and the humidity was very high. Any words of wisdom from those of you that might have had this problem?

The ignitor circuit also monitors the flame and if it 1) does not sense ignition or 2) senses flame loss, it will shut down the furnace. In my experience, this along with the high tension lead to the ignitor, are high failure items.

The furnace will not attempt ignition if the sail switch is inoperable.

Given your description, I suspect the board.

Good luck