I would like to replace my old thermostat with a new Ecobee3 thermostat. HVAC system is a Slantfin Galaxy GG75 boiler - single zone. (No air conditioner.)
Current set-up has only a red and white connected from thermostat to boiler. (see picture). There are unused wires from thermostat to boiler.
Connection at thermostat is to "T" and "TV" terminals (though not labelled).
Need help figuring out how the connect the common wire and where...
Thermostat manufacturer has suggested everything from not possible to get another transformer, to get a ran/isolation relay... No consistency on the best solution. Help Please.