I have a goodman heating & air unit. The heater will not turn on. When I flick the switch for heat the exhast fan turns on, and that all. I've check the breakers, turned the a/c on and it works fine (blower come on). Also turned the switch for the fan from auto to on... blower comes on. Just not on the heater.

Does the igniter glow? Is the LED in the blower section flashing and if yes then how many flashes?

Most likely the igniter has gone bad or gas is not touching the igniter. Whatever you do DO NOT touch the igniter with your hands... that makes them break. Let me know the answers to the above questions and we can get this problem answered more clearly.