I have a 9 yr old Goodman GMPN100-4 gas furnace and the unit will not stay lit. The vent fan turns on, it ignites for 6-8 seconds then shuts down. 20 seconds later, it re-ignites for 6-8 seconds, then shuts down. It repeats this 4-5 times, then stops. During this cycle, the vent fan stays on. After the last ignition cycle, the vent fan shuts down. The unit then never restarts. I can reset the power to the unit, and this whole cycle will repeat. I see no blinking from the diagnostic LED on the control board.

Does anyone have any thought about a failure mode? Thermocouple? But why no blinking from the LED? Anyway, any help is much appreciated.

You might try cleaning the flame sensor. They look something like this. Use steel wool or sand paper to shine it up. Easy does it near the ignitor since they can be easily broken and never touch the black/dark grey area of the ignitor.

That did it. Thanks very much! I saw that and figured it was a thermocouple and thought it was the problem. The absence of a "no ignition" diagnostic code (or any for that matter) had me questioning that. Thanks again!

Glad you got it going.