I have an older gas furnace, heat-only, with a 2-wire thermostat to an old Honeywell mercury switch. Wire colors are not to code, but work in any configuration with the old Honeywell thermostat.
I have a Nest generation 1 thermostat. I installed it with a 24V power supply. All good with power (no error messages). I installed on e of the old thermostat wires into the nest. No W wire detected. I tried it with the other thermostat wire. No W wire detected. Wires are clean and straight. When inserted into the nest wire holes, paddles stay down (confirming wire is in place)
The thermostat wires work. I can short them manually to call for heat successfully. I can hook them up to the old Honeywell switch and they work. Voltage through the old wires is 24V.
Any suggestions?
