BREAKING United #UA914 is declaring an emergency and holding 17,000ft. live:

UPDATE #UA914 diverted due to seat 1A entertainment system overheating, no fire.

UPDATE Reports suggest that #UA914 diverted to LHR following issue with air conditioning vents.

UPDATE #UA914 has 209 customers and a crew of 10 on board, diverted to LHR due to a maintenance issue.