As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO CLT DUE TO A VENT EXTRACT FAULT AND THE OUTLET VALVE STUCK OPEN PREVENTING THE AIRCRAFT FROM PRESSURIZING. THE AIRCRAFT LANDED SAFLEY AT CLT WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE SKIN AIR VALVE PER AMM 21-26-53 AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK.