My carrier weathermaker 8000 is 19 yrs old I had the same problem on and off during the cold weather. The Flame Sensor is not red and lit up the flame, in the past I just replaced the Flame Sensor and then it worked. This time I did replace the Flame Sensor, but it is still not working or lit up the flame. It is possible the electric circuit board bad, I had the technician replaced it about 6 yrs ago. It cost me $375.00. What should have to do ? Please help I haven't had the heat since 24 hrs ago, I temporary use the portable electric heater just to keep my family at night.