I have a goodman HVAC system model number GMNT080-4B and it won't heat. Opened the upper portion and the propane is getting lit by the lighter and runs for about 5 seconds. Then shuts off and goes through the cycle again and again until I turn the system off. Opened the bottom and the circuit board (white rodgers 50T35-730) has solid light which from my web searches is a good thing. Fan works when system set to fan on. Any ideas?

Remove & clean the flame sensing rod. Clean the metal rod part with fine steel wool or a Scotch Brite pad.

Grady White, you are the man. Furnace is running again.

Common problem with a simple fix. Glad I could help.