As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAH - FLT 3680, Pilot reported that the landing gear would not exctend on the first attempt. The gear was eventually extended and the aircraft landed at IAH without incident. Maintenance removed and replaced the landing gear solenoid valve. The landing gear sytem operationally checked good and the aircraft was approved for return to service.