The Goodman gas furnace has an automatic ignition system that doesn't require manual lighting of the pilot light. When the furnace lights, the glow ignitor starts first and the pilot light automatically ignites. If the glow ignitor comes on but the furnace doesn't fire up, some inspection and troubleshooting can be helpful.
Gas Supply
The Goodman furnace may not be receiving an adequate gas supply if the glow ignitor turns on, but the furnace cannot ignite. Find the gas supply valve next to or behind the furnace and rotate the valve to the "Open" position, typically by twisting counterclockwise. Stop immediately if you smell gas. Turn the furnace off and leave the house. Call your gas company or emergency services for help.
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Proper Ignition Sequence
When the Goodman furnace has lost power or was turned off for servicing, the proper sequence must be followed to relight the pilot light and fire up the furnace. Turn the furnace power switch to "Off" and the external gas valve to "Off" as well. Adjust the thermostat to the lowest possible temperature, then open the access door and turn the internal gas control knob to "Off." Wait five minutes so gas can clear out of the lines and smell again for gas before continuing. Proceed if no gas scent is detectible and turn the internal gas control knob to "On." Shut the access door, open the external gas valve and turn on the furnace electrical power. Move the thermostat back up to the preferred heat temperature. The furnace should now fire up as expected.
Flue Pipe System
If the Goodman furnace still doesn't light at the burner level, even after ensuring the gas supply is on and the proper ignition sequence was followed, turn off the furnace and ensure the furnace is cool. Open the access panel and look at the flue pipe system leading to the burners and pilot light. Carefully examine the flue pipe system for an obvious obstruction and clean away any debris. Don't adjust the flue pipe.
Air Intake System
Sometimes an obstruction in the air intake system can prevent proper ignition as well. Look at the intake pipe system, which usually enters the furnace near the top on downflow units or horizontal units or near the bottom if the furnace is an uptake model. Check for obvious signs of blockage and clean, if possible. Contact Goodman if you don't see any obstructions in the air intake system, flue pipe system or other troubleshooting steps don't get the furnace working. You may need to repair or replace the heat exchanger or burner.