My thermostat is in the basement, connected to a Honeywell R845A to run a circulating pump for heat. I bought an Nest E for the main house and it works great. I want to replace the thermostat in the basement also with a Nest E.
Someone suggested to use a plug in transformer to power the thermostat, which requires 2 wires, but I called Nest and they told me you can only use 1 wire to the "C" terminal.
In the R845A I have the two wires connected to the old thermostat.
Is there any way I could connect the plug in transformer by making it into a single wire "C" or is there any connection I could make in the R845A?
Best Answer
The Honeywell device does not provide a C wire out. There is fairly open access to it; perhaps you can pull a rabbit out of a hat.
Otherwise add a second transformer (2 wires from this new transformer). Phase it correctly, I discuss how to do that here.