Half of furnace turned off

This isn't a great answer but I want to provide something in case it helps others.

There was no issue with my flame sensor or the ignition device. It went on just fine but was kicking off due to some other reason.

After a lot of troubleshooting it was fixed by one of three reasons:

• powering off the furnace for a couple hours with thermostat disconnected.

• installing new thermostat. I was due for a new thermostat and not sure what could have been wrong with the old one. It did run out of batteries right before this but it doesn't make sense that when I left the old thermostat it worked fine with the furnace cover off. The only thing I can think of is the old thermostat was sending incorrect signals to the furnace that caused it to need more air during usage (maybe an AC expert might be able to give a plausible reason for this).

• Reseating cover with slight gap. I have since put this fully on but left it with a slight gap the first couple of weeks.

I did nothing else to the unit and the unit was in otherwise pristine condition - only a couple years old.

Some of the older Goodman furnaces was equipped with a flame sensor it was just a solid metal probe with one attached wire and when it heated up it caused a small millivolts in the probe if this sensor fails your furnace will not light or will go out after a few seconds, only maintenance required is cleaning the metal probe with steel wool or sand paper and check for a loose terminal due to heat stress its cheap and inexpensive to replace so it should be replaced every 5 years most problems with these probes were burned wires and connections as they are directly in contact with the burner (NOTE) Goodman furnaces were designed to run a few seconds in order to give the flame sensor time to heat up and produce the electrical current to activate the switch if no activity is sensed the burner will shut off, a flame sensor works on the same principal as an expansion thermo coupling except there is no movement on a flame sensor it works on millivolts of current generated by heating metal where as a thermo coupling has a mechanical rod in the housing that moves with heat expansion and stays as long as the pilot is burning,