A friend is traveling (with her housemate) and I offered to go feed her cat and give him some people-time each day. Her original flight was delayed to Sunday, so I made my first visit Monday morning.
It was 39 degrees in her house. The thermostat said it was holding at 60, but...no. I walked around the house checking for open or broken windows (none found). I went down to the basement and stared at the furnace -- no error codes or blinking lights, one steady light (so it had power), and that exhausted my knowledge of furnaces. I fed the cat, cycled through the thermostat programming to double-check things, reset the hold, built up some warm places to burrow, and tried to reach my friend (who was several timezones west of me, so I didn't expect an immediate response). I asked if she minded if I brought her cat to my house if we couldn't figure out the problem.
When she got my message she asked if the power was out (no, there were lights), and we speculated about whether power had gone out and come back on. I said I'd look for blinking or wrong clocks when I went back. Offhandedly, she wondered if a power outage would have somehow turned the thermostat off -- had I noticed if it was on? Um, I assumed it was because it showed me programming and let me set a hold temperature, and my thermostat doesn't let you do that if it's not on, and also it would be dangerously bad design if a power outage killed your post-power-resumption heat. So I went back later, and sure enough, the three-way toggle (cold - off - heat) was in the "off" position.
It's a physical switch, so I suspect my friend and the other person living in that house are going to have Conversations. Ouch. (Also, no blinking or very-wrong clocks.)
I turned on the heat and waited for the temperature to rise several degrees to make sure everything was on track. When I left last night the house was up to 45 degrees and the cat was very friendly. This morning everything was fine -- up to 65. (Yeah, maybe I overshot a little on that hold, but...)
Here's the scary part: originally they were going to leave on Friday, when the daytime high was 3F and the temperature was sub-zero before Shabbat started. When we were making the original plans, she'd said she'd feed the cat Friday so I didn't need to come until Saturday, and I said I wouldn't be able to come until Saturday night and that was fine with her. Friday night was frigid-cold here. I shudder to think what temperature the house would have been on my first visit if her flight hadn't been cancelled.