The inductor motor starts only when R and W are shorted on the control board. The wires to the motor do not have power otherwise. The fuse seems good though I'll be replacing it tomorrow just to make sure. When the thermostat is plugged in and tries to initiate heating, VRW=28 V. Shorting R and W with alligator clips does start the motor so it doesn't seem to be a control board problem, at least on the high-voltage side.
I do not know exactly what to expect when checking the wires behind the battery-powered thermostat but shorting RH and W there does not start the furnace. RC is left open for some reason, though the manual says that it should be shorted with RH. We have no A/C and nothing outside so there shouldn't be anything else between the thermostat and the terminals on the board.
The furnace was working normally last week but we're moving slowly so no idea when it may have stopped. The only "unusual" event since is that we switched the breaker off and on last week.
Where is the problem likely to be?
Best Answer
If connecting R and W at the furnace turns on the heat and connecting R and W at the thermostat does not then there's a problem with the wire from the furnace to the thermostat.