When I came in the valve had repaired itself, we now have a spare valve if it happens again.
Symptom: When the compressor shuts off you will hear a hissing noise as pressure in the compressor is vented, this is so next time it starts its not fighting a pressurized piston.
This hissing should stop in less than a minute.
If the hissing keeps going and never stops, the check valve is stuck - post to the board and it can get repaired.
Tom