I have a Goodman GMP125-5 and the fan runs all the time even with the thermostat off and the fan to auto. The gas never comes on. The only way to stop it is to turn off the power to the unit. I have done the following.

Circuit board LED blinking 4 times so I tested the overlimit switches. All are in closed and in testing the overlimit circuit from the board to the gas valve it showed a closed circuit on my VOM.

Tested the pressure valve by turning the power to the unit on so the inducer motor would start and the pressure value switch closed. I assume this switch is "open" when the motor is off and "closed" once the inducer motor comes on and creates enough pressure on the valve.

I feel I have eliminated both the overlimit safety (closed circuit) and the pressure switch (closes once the inducer motor is on) as issues so why do I still get 4 flashes on the LED?

Any ides on what I should check next? Is there any way to test the circuit board?