As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) FLOW LITE ILLUMINATED ON CLIMB, CABIN CONTINUED TO DEPRESSOR AND AFT GALLEY DOOR LIGHT ILLUMINATED PRIOR TO DESCENT. AIRCRAFT LANDED BACK TO YYZ. MAINTENANCE FOUND LT PACK FLOW CONTROL VALVE INOPERATIVE. FLOW CONTROL VALVE REPLACED AND SYSTEM CHECKED SERVICEABLE.