In January 2006 I had a new furnace installed ( a coleman gas furnace Model # BGAA070BDTBJ) and this ran fine throughout the rest of that winter. Early in the summer our thermostat went out and I installed a new Hunter thermostat # 42999 and I hooked it up as shown in the directions and it worked great with the central air all summer. Last weekend I tried to turn on the heat and this worked throughout 1 cycle then it kicked off and did not come back on even though the temp in the room was much colder and should have kicked back on. I looked inside the door for the furnace and seen that the indicator was flashing 3 times and according to the diagnostic panel this means - Combustion air switch failed to close. Is this something that is easy to fix or should I call someone. The furnace is under warranty still.

If it is under warranty, call somebody. It may or may not be an easy fix, and shouldn't have anything to do with the thermostat.

Thank You for your quick response. I have called the service person that installed the furnace. Once again, Thanks.