Hello,
I have a concord 80 plus furnace model C2E24A-2A. Thermostat control mounted in my hall way is a white-rodgers model 1F78. I have it set on auto for 70 degrees. Lately I found the temp. has fallen to 66 or below 70 and the furnace has not kicked on. I then will have to turn the thermostat all the way off for a few minutes and then turn it back on. Even then sometimes I will have to flip the controls around to get it to start. The furnace is about 5-6 years old. I had it serviced 2 years ago.

The thermostat may not be the problem. A malfunction may be causing the furnace to initiate a timed lockout, and cancelling the thermostat demand may be cancelling the lockout. If the circuit board has a status light, it will provide clues.