SYMPTOM:
No heat. There is 24v between R and C on the control board. No power between W and C on the control board. Thermostat is set to heat and temperature is set to above room temperature.
SOLUTION:
Put a jumper from W to R on control board. Furnace should run normally. Remove jumper from board. Remove R or RH wire and W wire from the back of the thermostat and install jumper between them. If furnace runs normally replace the thermostat. If it does not run check wiring from thermostat to furnace for a loose connection or replace wiring. It is possible to take thermostat beside furnace and use a short wire to connect it to the furnace board until a new wire can be ran.
