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I have a couple Nest thermostats that I want to power when my boiler is powered off.

My plan is to hook them up to a 24v transformer using the existing R/W wires (no C wire and I don't want to run one) and just disconnect the wires from the boiler to that.

My question is do I need to add a resistor or some load to the circuit as it will just be going from the transformer, to the nest, and back to the transformer? enter image description here

  • What are these Nests doing? – ThreePhaseEel Aug 16 '16 at 22:33
  • The Nests aren't really doing anything other than logging the temperature and being a clock – kbickar Aug 16 '16 at 22:38
  • What's controlling the boiler, then? (Also, is this a hydronic or a steam system?) – ThreePhaseEel Aug 16 '16 at 22:39
  • During the winter months, the boiler (steam) will be turned on and wired into the Nests - added image to explain – kbickar Aug 16 '16 at 22:40
  • What the heck on the steam boiler is the Nest trying to control? Steam boilers typically aren't connected to any sort of thermostat -- instead, there's a vaporstat or pressuretrol on the boiler that controls system pressure, and then there are special thermostatic control valves on the radiators that control local temperatures. – ThreePhaseEel Aug 16 '16 at 22:51

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