As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ON DEPARTURE, A/C WAS CLIMBING THROUGH FL210 WHEN THE CREW NOTICED THE CABIN DIFFERENTIAL WAS AT MAXIMUM AND THE CABIN RATE OF CLIMB WAS EXCEEDING 3000 FPM (UP). THEY IMMEDIATELY INITIATED A RAPID DESCENT AND STABILIZED THE CABIN ALTITUDE AT AN A/C ALTITUDE OF 17,000 FT. THE A/C RETURNED AND PERFORMED A NORMAL LANDING. MAINTENANCE CARRIED OUT T/S AND REPLACEMENT OFTHE PRESSURE CONTROLLER.