York gas furnace problem - Won't stay on.

[rbf3999]

My gas furnace comes on when I cycle the switch of the thermostat from "off" to "auto". The heat runs for a while, but does NOT get up to the temperature it was set, and then shuts off until the next time I do the above mentioned. If I leave it on "auto" it does not turn on again at all even though the desired temp is supposed to be 69. I have replaced my thermostat, had same problem, and replaced my theromostat again, same problem. It seems to me it must be the thermostat, but logic is telling me I cannot have three bad ones at the same time. What else should I check?

[Robert]

Hi,

Would need to start at t-stat and using wiring diagram, test the circuit components and wiring to find break in circuit not allowing furnace to operate as designed.


Thanks,
Robert