furnace issues

I would not just run out and buy a new battery. Take the old one out and have it tested and fully charged. Most locales will test the battery for free. Some will put on a charger without any charge.
Then if it is bad, get the new one in the spring. At least then you will know.

I appreciate all the responses, I will get a new battery in spring and try that. Thank you all

Agree with the above. Blower needs to turn fast enough to trip the sail switch.

Just in case it hasn't been said it sounds like a low battery.

Okay yes I know I'm really number 6 saying low battery. :) I do second hooking up the jumper cables from your tow vehicle (positive to positive and negative to trailer frame) Start the tow vehicle and then test the furnace.

enblethen wrote:
I would say you are experiencing low voltage to the furnace. low voltage would cause the fan not to run fast enough to operate the sail switch.
When running on shore power the converter is putting out higher voltage.
I would have battery tested, clean the connection on battery good and then check to see what voltage is getting to the furnace.

+1
Make sure the battery water level is proper. Remove the cables and clean the battery posts and the clamps with a wire brush.

Agreed...weak battery. Another way to test it without the theory that the 120 V shore power is using some other ignition system, would be to hook up jumper cables from your tow vehicle to the battery in the trailer, and see if that gives you enough power to run the furnace.
I hooked up a digital harbor freight three dollar multi meter inside my tiny trailer with the sole purpose of determining at what voltage will my furnace stops working. Well I don't have the answer yet because I fell asleep when the voltage was down to 11.2 last time I remember looking. This experiment was well running off an old battery from a junk car.

Lights and water pump will still operate on lower DC voltage.......

Furnace.....low on battery voltage and several components will not properly work

Remember it worked fine that weekend for awhile then stopped.........battery had been drawn on (especially furnace which is a DC Hog) and voltage went low enough to cause issues with furnace but not other dc items.

Then you used shore power...AC Voltage converted to DC voltage (converter output 13.2V DC and higher).

Charge up battery.....full charge and try furnace again.

Welcome to RV.net!
There is only one ignitor.
I would say you are experiencing low voltage to the furnace. low voltage would cause the fan not to run fast enough to operate the sail switch.
When running on shore power the converter is putting out higher voltage.
I would have battery tested, clean the connection on battery good and then check to see what voltage is getting to the furnace.

The lights and water pump all work fine on battery, are there two igniters for furnace,one for battery and one for electric or oonly one

Bad battery