I would like to know if I can use a Nest Thermostat with my system.
I have a gas-fired steam boiler with a 24V transformer and a Lux 1500 thermostat. The Lux thermostat was using only W and RH. The Google Nest Thermostat compatibility tool told me I could replace the Lux with the Nest Thermostat if I ran a C wire from the transformer to the Nest. I made all the connections as instructed (W, R, and C) but something shorted out on the boiler and now there’s no 24V power at the transformer. (I’m assuming that I’ll be able to get power back with help from my heating guy. But he’s not very familiar with the Google Nest Thermostat so I’m asking about that here.)
I pulled out the wiring diagram. There are two anomalies. First, the thermostat wire had been connected to W and RH on the Lux. However, the wiring diagram indicates that the thermostat sits between the Y terminal on the transformer and G on the transformer. The G on the transformer then goes through the Low Water Cutoff and back to R on the transformer. There are other controls and switches in the circuit, too. Secondly, ChatGPT suggested that I can’t use the C wire terminal on the transformer with the C terminal on the thermostat.
Here's the wiring diagram. I would really appreciate help with this, it is different from what the compatibility tool told me. Is there any way for the Nest Thermostat to work with this system (once the power is restored)?
(Note that this boiler has a hot water loop for a tankless water heater but that loop is not controlled by the Lux thermostat.)
Thanks.
Note: I have not installed a Nest thermostat in one of these boilers, so proceed at your own risk.
I found the installation manual, and this is what it has to say.
