Furnace not Shutting Down Properly

I have a York Diamond 80 furnace with a newer main board. The furnace worked great all winter and just started having issues this morning. Here is what happens.

1. I power the unit off for 20 seconds to reset the board.
2. I turn back on and the thermostat triggers the start of the sequence.
3. The furnace works as expected and runs for the usual amount of time.
4. It begins its shutdown sequence and turns the main blower off.
5. The flames never shut off and continue to go until it triggers an overheat shut down I believe.
6. The trouble shooting light now starts blinking red, 4 blinks and a pause. “Open High Limit Switch” is the error code.
7. At next power on cycle the exhaust fan kicks on, but the flame igniter never glows and the gas never turns on.

I find it odd that the flames continue after the blower shuts off.

Any thoughts?