Thermostats are very reliable controls, and it's rare that
anything actually goes wrong with the thermostat itself. It's
far more likely that something else is preventing the heating
system from coming on. Thermostats work on 24 volts AC, whereas
the rest of the circuits in your house are 110 volt AC. So,
there will be circuit breaker in your house's breaker panel that
provides power 110 volt AC power to the heating system and a
transformer that converts that 110 volt AC power to 24 volt AC
power for the heating system to use. So, the first thing to do
is check that the circuit breaker for the heating system isn't
tripped, and the next thing to do is check that the transformer
for it is producing 24 volts AC at the output terminals. If you
have 24 volts AC at the output terminals of the transformer,
then you should be getting 24 volts AC at the gas valve of the
boiler or furnace when you turn the thermostat up. If you don't,
then the problem MAY be the thermostat itself, but it's more
likely to be one of the