I am trying to replace a broken thermostat. It is a 3 wire White Rogers, one of three zones to a hot water boiler heating system. One wire is red, one is blue, and the last is white. Every thermostat (programmable) I buy has slots for 4 wires. Can I leave a slot open? I don't have a cooling system.
For a three wire zone valve, the stat needs to have a contact that closes when when the call for heat is complete. The zone valves power open with a call for heat and power closed when the call for heat is satisfied. The average 4 wire digital heat and cool stat will not work for this application. There are some that will accomplish this but are usually more high end.