Honeywell Digital "Round One" thermostat. I think it's a CT-2700 but I'll
have to check. It's the one with simple two step programming.
The question is: Is there a battery in it? Something keeps the clock
going when the furnace is off and there's no 24VAC, right? I don't think
it could go too long on a capacitor alone. There's something on the PC
board that could be a battery but I haven't probed it with a DMM yet.
It doesn't look replaceable--are you supposed to toss the stat when it goes
bad? Ours is starting to have a flaky display where some segments of LCD
numbers aren't working. Then again sometimes it's fine. I was thinking of
taking a watch battery and (if I can solder to one without damage) stuffing
that in there as a replacement. I can always hang a conventional cel
outside temporarily as proof of concept. I mean the stat should normally
be powered from the 24VAC so one would presume a bad battery would only
cause loss of time when its off and not weird display artifacts at normal
times but who knows.