I have a Goodman Furnace GMH8 that is 4 years old and has been working fine but today it will not stay lit. The furnace lights for about 2 seconds and then goes out. The blower comes on and will continue to run as the furnace lights and then goes out several times before shutting off.

That problem is fairly typical of a blocked vent pipe or a cracked exchanger. Sounds like the rollout sensor is tripping. Make sure the exchanger is clean and not cracked and that all flue vents are open. I would also make sure the flame sensor is clean. Remove and polish with steel wool or light sand paper. If the flame comes on it shouldn't be the ignitor.

Thanks ma0641, the flame sensor did the trick. I have heat again.