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Nest thermostat misfiring steam boiler
I'm posting to inquire if anyone had the same problem as me. I have a 3rd generation Nest that I would like to use to control a high-velocity forced air system for AC (wires Y1, G, Rc, and C) and a Burnham steam boiler for heating (wires W1 and Rh). When I only connect the AC system, all is good. The Nest uses the C wire to power itself. I measured the that C wire provides 28 VAC with a multimeter.
When I also connect the steam boiler, the Nest does not work properly. It intermittently closes the loop of the boiler every few seconds, which makes the relay click. Obviously, the Nest has decided it wants to steal power from the steam boiler even though it has a live C wire.
My plumber had suggested that maybe the wiring between the steam boiler and the thermostat was defective. I did a continuity testing and also have been running this winter with an older Honeywell programmable thermostat (connected only to the heat - wires W1 and Rh). It fires the boiler when it should and keeps it shut when no heat is called.
Has anyone encountered this similar, and rather weird, problem?