[Scene: I'm sleeping.]
"Is the furnace broken?"
It does in fact seem chilly.
Downstairs.
There was an LED light.
3 blinks.

WTF is a pressure switch?
Could it be the leaking freon that we haven't addressed?
We need an AC person. The home warranty seems to be very lacking. Recommendations?
— /🏴\ stLouIST (@stlouist) August 14, 2019
For the furnace?
I am armed with a lighter and a flashlight.
Update: after some research and some tinkering...
Inexplicably, the furnace has decided to work hours after I took the hoses off and put them back on. Pressure switches, amirite?
— JW (@jeffwiegand) February 3, 2020
More later as I put together an RFP for our HVAC System.