I have a General Controls Thermostat Catalog number T-231C100A108. This thermostat controls heat and a/c although the A/c side has never been wired. The heat side requires that the furnace turn on, the water pump start pumping water through the pipes and also activates a fan located inside each rooms heating unit. The fans can be adjusted locally. It is 24 volt andI see four screws with wires F red wire, C white wire, V appears to be black wire and H appears to be a blue wire. The ac side is Z and D no wires attached. It is a stainless steel rectangle app. 3 inches high and 4 inches long and an inch or so deep. Tow number wheels show through the front heat and a/c (the a/c is not used. There are two slide dial that control the Fan and the Heat. In automatic the fans go on when the heat goes on. I would be willing to replace with an identical model or a newer thermostat but do not know how to wire to a new thermostat.