As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNABLE TO PRESSURIZE, DUMPED FUEL AND RETURNED FOR LANDING. TROUBLESHOT, FOUND INSULATION BLANKET OBSTRUCTING LEFT HAND OUT FLOW VALVE. REMOVED OBSTRUCTION AND CLEANED OUT FLOW VALVES PER MM 21-30-11. AIRCRAFT PRESSURIZED OK PER MM 21-30-0.