Replacing a manual thermostat?

I question the wisdom of having a timer on a boilet. It takes more to reheat it thanyou save unless you turn it off for a whole day or more. I also question the economy of turning back a thermostat more than once a day. OK a new thermostat sounds good. some have batteries and don't need the third wire. see how many wires you have before spending money for something you can't use. Some older thermostats were wired with only two wires.