Is there a direct train connect from Heathrow to Bradford on Avon, or must one go to Bath and then connect somehow? Leaving tomorrow, please respond if you have the answer. Thanks!
No, the only trains from Heathrow go into London (train to Paddington Station, or the Piccadilly tube line).
Trains to Bardford on Avon go either from London Waterloo (slow, direct trains), or London Paddington (faster trains with change of trains, not always at Bath). Since you are starting at Heathrow, Paddington will be better.
You can look up times at the National Rail site: http://www.nationalrail.co.uk/
What about the Railair coach to Reading from Heathrow, then a train to Bath from there, saves going into London.
You could take a National Express coach from Heathrow to Bath and then connect to Bradford-on-Avon.
same answers you got in August
https://community.ricksteves.com/travel-forum/england/train-from-heathrow-bradford-on-avon
That is truly weird.