As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE LEFT MLG RED UNSAFE LIGHT REMAINED ILLUMINATED WITH THE YELLOW GEAR DOOR LIGHT ON AFTER GEAR RETRACTION LEAVING IAH. CYCLING THE GEAR DID NOT HELP. THE AIRCRAFT WAS RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED THE LEFT MLG RETRACT CYLINDER PER MM 32-32-02. A GEAR SWING WAS PERFORMED AND ALL OPERATION AND INDICATIONS CHECKED GOOD.