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Powering Nest Thermostat from different power source
Hypothetical question. If you have a Nest controlling central AC and a zone for heat at a boiler .......
Can you connect the C terminal in the Nest to a relay with a common at the boiler ? Meaning ..... RH , W and C of the Nest would be powered by the zone relay, like a Taco SR501 . R , G and Y would be connected to the AC equipment.
Have a job where theres one unused wire from the thermostat to the boiler. No extra wire to the air handler and no wire connected to C of the current thermostat.