Hello! I installed two nest learning thermostats to replace honeywell switch thermostat. Heat only propane water baseboard system. So I have red and White wires connected to Nest Rh and W only.
The nest thermostats work but intermittently have power failure (e74 wiring error). I *think* need to connect up a nest power connector, but I am confused about how to properly do this with the Taco 404 controller relay board. There are no "R", "W" or "C" labels on the board. the thermostat switch lands on "T" lugs.
I tried to wire in the nest power connector with the R&W wires in-line as normal, but I'm confused on whethere to land the C wire of hte nest power connnector. Tried with C wire to the left as well as to the right lug of 24 V power terminal, but neither seems to work. The zone LED lights up "dim" when demanding heat.
Thanks for reaching out ― let's see what's going on.
Give these steps a try:
Keep us posted.