I have a Regency GCI 60 Insert and I have an issue were the fire dies out and the blower goes off and then the 3rd light blinks. When I open the Hopper door the blower kicks back on and after the door is closed the blower shuts down again and then the 3rd light on the control panel blinks. The manuel states when the 3rd light is flashing (the exhaust temp. switch contacts have opened. what is causing this to happen?