As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LANDING GEAR WOULD NOT RETRACT AFTER TAKEOFF, HYDRAULIC PRESSURE LIGHT DID NOT ILLUMINATE. GEAR INDICATION WAS 3 GREEN AND NO RED. REMOVED AND REPLACED SUSPECTED FAULTY LANDING GEAR CENTER BYPASS VALVE AND PRESSURE RELIEF VALVE. PERFORMED LANDING GEAR RETRACTION AND EXTENSION, SYSTEM CHECKED GOOD. ALL WORK PERFORMED IAW CESSNA560 MM CHAPTER 29-11-06 AND 32-30-00.