Thanks for the suggestions, Ex-Tech. Those are good ideas, but I don't know if any of them would explain why the furnace lights reliably when the cover is off.
The battery voltage is ok, but aside from that, I've been doing this testing with the trailer hooked up to AC power. So the furnace has been running off the converter DC output.
If the sail switch or fan motor were defective, the propane valve wouldn't open, correct? (and the fan blows out air, so that seems fine)
The furnace goes through a normal start-up procedure: the fan starts up, the propane valve opens, and the ignitor attempts to spark. The only thing that's not happening is that a spark is not actually being generated -- when the cover is on.
I think I'm going to replace the ignitor. It's only $10 and is easy to replace. I will also check the burner for mud daubers and other debris -- I hadn't thought of that.
Any other thoughts?
Many thanks,
Dave
