Hi, I have a Rheem forced air Natural Gas heating system, I can not find a model number, but it says "Imperial" on it and I'm guessing it is aprox 15 years old. What is happening is that when I turn the heat up, it tics then the fan starts up but no flames start in the furnace. Therefore all I get is cold air. The electric pliot lite seams to bw working but the flames never start. Please help me if you can. Thanks for your time.

If the pilot is firing upand the main burner doesn't start it is a dirty flame sensor, bad ignition board, or gas valve.