Furnace won’t light

[brooks340]

This morning our furnace won’t light. Fan runs but furnace doesn’t light so fan cycles the shuts off. I opened the outside furnace door and I see the red led blinking once every three seconds, which indicates and airflow/limit fault. When I power cycle the furnace with the reset switch it ignites like normal, but won’t ignite again without another reset. It’s a Dometic furnace in a 2020 294RL. Any ideas?

[Slow Hand]

Originally Posted by brooks340

This morning our furnace won’t light. Fan runs but furnace doesn’t light so fan cycles the shuts off. I opened the outside furnace door and I see the red led blinking once every three seconds, which indicates and airflow/limit fault. When I power cycle the furnace with the reset switch it ignites like normal, but won’t ignite again without another reset. It’s a Dometic furnace in a 2020 294RL. Any ideas?

If you run out of gas than it will take some time for the gas to reach the furnace. i had this problem a couple times and found if you run out of gas then you need to open the full bottle then switch to the full bottle then close the empty bottle. If you have a automatic switch than you need to leave both bottles open all the time. There is something in the system that won't allow the furnace to come on when the pressure gets to a certain point. That way the fridge will still work. The bast way I found is light the stove and let it run for a couple minuets then the furnace should light.

[brooks340]

Thanks for the reply. Both propane tanks are full and the furnace ran fine until this morning. Both water heater and stove also work fine.

[DQDick]

Dometic is notorious for bad sail switches. Yours could be sticking, clogged with animal fur or just plain bad.

[sourdough]

My last trailer did that exact same thing a few months after we purchased it. Initially I went and reset it outside so it would make a heat cycle, then start up and shut down. Then found I could just turn it off then turn it back on and it would do the same thing. The solution was to replace the control board. Don't know if that is your issue but it cured our problem.

[brooks340]

Is the sail switch something I could check myself?

[sourdough]

The sail switch is apparently a common problem. I know on this one (not the previous trailer) they had to replace the control board as well after the 1st outing. It just stopped working completely. On both occasions they thought it might be the sail switch but it wasn't. I don't know which furnace you have but here is a quick video of a Dometic I believe judging by the exhaust port which may be of some use. I'm hoping you have that kind of access since if not you will probably have to remove the furnace from inside the enclosure;

https://www.youtube.com/watch?v=IUniqYY-Ohc

[brooks340]

So I removed the sail switch and it looked fine. I opened and closed the switch a bunch of times and blew on the contacts hoping to remove any dust or lint. I then reinstalled it and buttoned up the enclosure. The furnace now seems to operate like normal. Switch may still fail again but for now it appears to be working. Thanks for all your help on this one. Safe travels.

[ChuckS]

Too bad you didnt use an ohm meter and ohm across the two leads as you actuated sail switch back and forth to verify the overall resistance across the contacts of the sail switch... most likely it has quite a bit of resistance across it... the switch contacts are sealed inside a case so no easy way to try and burnish them ... most likely you will need a new sail switch pretty soon... Id order one to have on hand