As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED; "VENT AVNCS SYS FAULT" ECAM MESSAGE CAME ON. LEVELED OFF AT 10,000 FEET, DECLARED AN EMERGENCY AND RETURNED TO BOS LANDING SAFELY. REPLACED SKIN AIR OUTLET VALVE PER AMM 21-26-53, ACCOMPLISHED SATISFACTORY OPERATIONAL CHECK.