We woke up to find it was 61 degrees in the house this morning. The thermostat is set to be a little cooler overnight, but not this cold! We checked the breaker and other switches, but the furnace was dead as could be. We called for service, and after the very nice gentleman asked us about the breaker, etc., he asked if we checked the batteries in our thermostat. I was sure that wasn't the answer; after all, the display on the thermostat was working fine, and if the batteries weren't working, wouldn't that be gone too?
So, we checked the batteries - we needed AA, and guess what's on our grocery list for today? We had only one AA in the "battery drawer," and we needed two. I was starting toward one of the TV remotes to get a second one, but DH wouldn't hear of that! Instead, he went to the bathroom scale, as he had just replaced the batteries in it (he moved really fast so I would leave his beloved remote controls alone!). We put in the new batteries, and voila! The furnace kicked in and is now nicely warming the house. I guess just because you can see the read out on the thermostat, it doesn't mean the batteries are good. Who knew?