As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - ON DEPARTURE AIRCRAFT FAILED TO PRESSURIZE. RETURNED ORD WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. FOUND RIGHT FLOW CONTROL VALVE STICKING IN CLOSED POSITION. REPLACED RIGHT CONTROL VALVE. SYSTEM GROUND CHECK NORMAL OPERATION.