I learned a new lesson this morning.
The furnace won’t work if the programmable thermostat needs new batteries.
I confess, I thought the batteries were there just to hold the settings in case the electricity goes off. NOT SO!
The furnace was working when I went to bed last night. It’s set to drop to 64° during the night hours. (I stay toasty in my heated waterbed). It’s supposed to go back up to 70° at 7:00AM. When I woke up, the room temp seemed chilly.
I first checked the thermostat to see what it showed, and the display was blank except for the words “REPL BATT”.
I got out the instruction book and there it was: Heating/cooling system won’t work unless live batteries are installed.
Wouldn’t you know that the batteries decide to die when the outside temp is 5°!