As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AFTER TAKEOFF, LANDING GEAR WOULD NOT RETRACT. RAN QUICK REFERENCE HANDBOOK PROCEDURE. UNABLE TO RAISE GEAR. HANDLE WOULD NOT MOVE UP AT ALL, WITH OR WITHOUT USING TRIGGER OVERRIDE. EMERGENCY WAS DECLARED AND RETURNED TO JFK. REMOVED AND REPLACED LANDING GEAR BY-PASS SELECTOR VALVE PER AMM 32-31-51.