You guessed it. Got up to relieve myself at 5 a.m. and I just KNEW the furnace crapped out! On the coldest day of the year. I see the blue flame (starter flame?) pop up but it doesn’t catch. Totally failure on all 3 zones. All thermostats are fine too, btw, so that was a red herring.
I plumber who’ll stop over on the way to another job just to see if he can get the thing to start. Then he can come back for repairs. I'll take it.
Depending on what he can or can’t do and when he can come back, I may keep the Corolla warranty appt. At least it’ll be warm there!