On 8 February 2022, a Boeing 767-300ER inbound to Madrid at FL340 experienced a failure of automatic pressurisation control, followed almost three hours later by a failure of manual control and rapidly rising cabin altitude. An emergency was declared and descent made to FL120 where manual control was regained. The flight was completed without recurrence. The failure cause was found to have been water leaking from a tube with a broken clamp which, when it froze, had blocked the air conditioning outflow valve doors. Elements of the system design, scheduled maintenance requirements, and fault detection were identified as contributing factors.