I have a Colman Evcon Direct Vent Forced Air Furnace: Model number- DGRT075AUA. The furnace fires and kicks on, everything works fine if you turn the furnace on and off at the switch. The only issue is the thermostat will not turn the furnace on and off. It's a brand new thermostat, was thinking the issue was maybe a relay telling the furnace when to kick on and off.