Hello

Looking to replace the old Honeywell thermostat to another unit that is programmable. I have a gas boiler with water baseboard. No labels on the 2 wires on thermostat end. But on the boiler end I see 3 wires instead of 2 and they are labeled 1, 2 and 3. Any idea which is what in now days terms? The house is 18 years old and it has 3 zones (one per each floor). At the boiler all wiring color are connected to the respective numbers.

Thank you
Ermal G

If there are only two wires at the old thermostat, don't worry about the ones on the boiler. Just hook one of the old wires to r (or rh) and the other to w on the new stat and you should be all set.