[Sterling1970]

When I turn the heater on, it goes through it's cycles the electric ignitor glows hot, I can actually feel the solenoid valve open, gas goes through the piping and out the nozzles and ignites. Then in about two seconds, it shuts down. No more flame. The exhaust fan is still going and the main fan still blowing but no heat... What is going on?

[labman]

The control board is shutting the gas off because it is not getting the signal from the sensor that says the gas ignited. The sensor could be dirty, bad, or a bad connection. It may be a flat, round doodad with 2 wires going to it or long and narrow. It will be in the area where the flames are. Find it, clean it, check the connections and try again. No go, try a new one.

May have to invade an electrical or HVAC supply to buy one. Might try a hardware store first. They are usually friendlier to DIY. Often they are a round doodad with a diamond shaped bracket and 2 terminals. If they don't have a rating marked on them, you may have to take the model number of your furnace to a dealer for your brand of furnace.

Your detailed description of the sequence made it easier for me to answer.

[NorthernHeat]

Sounds like a dirty flame sensor, a small metal rod usually located in front of the far left burner. It is mounted typically by a ceramic piece, secured with a 1/4" zip screw. Remove the flame sensor and clean it with some fine steel wool or a piece of crumbled up aluminum. Using coarse sandpaper only scars the surface and causes the flame sensor to get dirty faster. As with all appliance be sure to disconnect the power before doing any repairs.