As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED, UNABLE TO PRESSURIZE THE AIRCRAFT IN AUTO AND MANUAL MODES DURING FLIGHT. RETURNED TO KBDL AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE GROUND AIR CONNECTION CHECK VALVE BROKEN. LOCKED THE VALVES OPEN AND DEFERRED THE VALVE. CMH MAINTENANCE CLEARED THE DEFERRAL LATER THAT DAY BY REPLACING GROUND AIR CHECK VALVE. OPERATIONAL AND PRESSURIZATION CHECKS WERE GOOD WITH NO FURTHER DEFECTS NOTED.