How do I add a "c" wire to the boiler for a Nest thermostat?

Question

I have a Lennox wall mounted boiler (gwm 075ie), I am trying to connect a "c" wire so I can install nest thermostats. I have 3 zones, currently running 2 wires (r&w). There is an extra wire behind each thermostat, that runs down close to the boiler, none of those wires are connected to anything. My current transformer is rated at 40va.

Unsure of the best way to do this. I have taco valves (z075c2-1) each valve has a "c" connector. Could I just run a wire to each of those connectors to the thermostat? Is the transformer able to handle 3 zones and 3 smart thermostats? Taco says a 40va transformer can run 12 valves.

Answer 1

Yes, that C connector on the valves is what you want. The nest thermostats use very little power, so that shouldn't be an issue for your transformer.

There are two wires coming from the transformer. On a typical HVAC system, the red wire is used for control, and the other wire is what gets used as the "common" or C-wire. In your diagram it looks like white is being used for control and red is going to the C terminal of the valves.