As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 523 - MIA-CCS - DURING CLIMB-OUT, CREW UNABLE TO CONTROL CABIN PRESSURE. OUTFLOW VALVE CLOSED DURING ENTIRE TIME. AIRCRAFT RETURNED TO MIAMI WITH NO EMERGENCY LANDING DECLARED. SWAPPED AIRCRAFT, FLIGHT DEPARTED TO ORIGINAL DESTINATION 3:45 MIN DELAY. TROUBLE SHOT PRESSURIZATION PROBLEM TO CABIN SAFETY RELIEF VALVE FAILED IN THE OPEN POSITION. REMOVED AND REPLACED SAFETY RELIEF VALVE. AIRCRAFT RETURNED TO SERVICE. (M)