Attached is the wiring of my system. I am attempting to upgrade my thermostat to a nest. My thermostat only has a “r” and a “w” wire. The nest thermostat said I required a “c” wire. There is a wire already run to my boiler but I am having trouble. I assumed “c” should be connected to the 24v ground on the control unit, but the nest still does not see power on the c wire. I read 18vac between r and c. I verified the wiring of the boiler is correct. What am I missing? Note: do it yourselfer, with some experience in electrical systems.
