As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GEG - FLIGHT 2371 - CLIMBING OUT OF 8000 FEET, PRESSURIZATION WAS RAPIDLY INCREASING, AND 12000 GOT A MASTER WARNING. AIRCRAFT WOULD NOT DEPRESSURIZE IN MANUAL MODE, DESCENDING OUT OF 10000 MANUAL MODE STARTED TO OPERATE. RETURNED TO THE FIELD AND ACCOMPLISHED A UNEVENTFUL LANDING. MAINTENANCE REPLACED THE AFT OUTFLOW VALVE. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.