This morning, my central gas heating unit did not automatically kick on when the temperature in the house got too cold. Instead, the house had sort of a burning (not smoke, more like a burned rubber/plastic) smell throughout. I turned the system off for about an hour while I searched for an answer, and when I turned it back on, it functioned properly. The same thing happened again this evening and I found that when I turned the fan to "on" instead of "auto," heat came through the vents. When I switched it back to auto, it continued to work. Any idea what might be causing this problem? Could it possibly be related to the thermostat? I'm sure the one on there now is the original thermostat (house is 13 years old) and I have wanted to replace it with a digital one anyway. Just curious if the thermostat might have anything to do with it. Thanks!

This morning, my central gas heating unit did not automatically kick on when the temperature in the house got too cold. Instead, the house had sort of a burning (not smoke, more like a burned rubber/plastic) smell throughout. I turned the system off for about an hour while I searched for an answer, and when I turned it back on, it functioned properly. The same thing happened again this evening and I found that when I turned the fan to "on" instead of "auto," heat came through the vents. When I switched it back to auto, it continued to work. Any idea what might be causing this problem? Could it possibly be related to the thermostat? I'm sure the one on there now is the original thermostat (house is 13 years old) and I have wanted to replace it with a digital one anyway. Just curious if the thermostat might have anything to do with it. Thanks!
My best guess is the blower motor failed (overheated) and once it cooled off it would run OK for a short while,