Got a call from the in laws. Their furnace has been acting weird so they called someone in. The guy checked things, tightened a loose wire (apparently the continous fan had quit running a couple of weeks ago) and came to the conclusion that the thermostat is on the fritz and they need a new one. They have an 80% two stage Carrier and the thermostat (Carrier) is a simple heat/cool mercury stat. The set up is all of three years old (heat & cool). Apparently, the temp in the house gets uncomfortably cool before the heat kicks in and then it heats past the set point before shutting down. I did notice today that the anticipator was set at ".3" which I think is pretty standard.

When they told me what the tech said about needing a thermostat, I kinda went "huh?". The thing is so simple I'm thinking "what can go wrong with it?". I took the cover off of the thermostat to have a look. The bimetallic twists back and forth, the mercury goes back and forth...what could be the matter?

Really, is this believable?