Flame Tip Sensor

Furnace Ignitor failure is a common problem that I see every year and I cant say that its one brand over the other either. The main reason why older gas furnaces (pre 1992) and water heaters go out is the thermocouple. The thermocouple senses the flame of the pilot. If the thermocouple goes bad it senses there is no flame and it shuts off the gas supply to the pilot, and the gas supply to the main gas valve. Great safety feature.
Problem: Your furnace burners light and the gas stays on for 8 to 10 seconds, then the flames go out and stay off.
Solution: First, turn off the power to your furnace. Next, remove the screw or screws that hold your flame sensor in. Clean your flame sensor with light sand paper, steel wool or emery cloth. You might need a new flame sensor, but most of the time they can be cleaned and your furnace will work well after cleaning. I have seen flame sensor go out. Most of the time when they go out the white porcelain is cracked. May Still need to replace the flame tip sensor.