is now working. The contacts in the thermostat, which turn on the furnace, needed sanding to remove some kind of residue.
These are the contacts inside the thermostat on the top left. I'm surprised after just a few weeks of use they needed cleaning, though I have been in the Casita
for several months before I ever turned on the furnace. I had fiddled with the contacts before, but they looked very clean. I guess there was some kind of build-up I couldn't see.
Thanks for all the help, and I'm glad it wasn't anything serious. It's scary having things stop working when it is below freezing.