My wife and I bought our house 3 years ago. It has two zones using Erie Zone Valves (I'll be adding one to make it three within a year or so) and is a Burnham Series 2 natural gas boiler. When we moved in, both zones used the old style mercury thermostats, with only two wires. Both zone valves are wired to an external 24v transformer that's mounted to my wall.
I have since pulled an 18/5 wire from my upper level thermostat down to my utility room, ready to go! I also bought the Ecobee3 thermostat, which I have on hand. At this point, I'm ready to try and connect the thermostat, however I have a few questions:
I have 4 wires, two black and two red. I know the two blacks are for the thermostat wiring and the reds are for the boiler wiring. Since I haven’t removed anything yet, I can make a wiring diagram and take pictures to get it back to where it was. I just am not clear on where the extra C-wire gets wired to. Do I just wire-nut it to the same lead that goes from the Zone Valve to the common side of the transformer and then pigtail those two to the transformer?
Any help is appreciated! Thank you!