As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF THE CREW OF FLIGHT 2401 NOTED THAT THE AIRCRAFT WAS NOT PRESSURIZING. THE AIRCRAFT RETURNED TO PHL AND MADE AN UNEVENTFUL LANDING. PSA MAINTENANCE AT PHL MEL'D THE PRESSURIZATION SYSTEM. THE AIRCRAFT FLEW TO CAK WHERE PSA MAINTENANCE FOUND THE PRIMARY OUTFLOW VALVE FAILED IN THE OPEN POSITION. THE VALVE WAS REMOVED AND REPLACED IAW CRJ 200 AMM 21-32-01-000-801 AND AMM 21-32-01-400-801. THE PRESSURIZATION SYSTEM OPERATIONALLY CHECKED GOOD AND THE AIRCRAFT WAS RETURNED TO SERVICE.