"Richard J." wrote:

Heathrow Connect's website says that "Pre-pay Oyster" is not valid, which
suggests that it might be an old comment that hasn't been revised. TfL's
site says that PAYG is valid between Greenford/West Drayton and
Paddington, which would include the section of HC east of Hayes. I've
emailed HC for clarification.

PAYG certainly is valid. Had to go out to Hayes & Harlington on business
last week, and there are multiple validators at the station. As it happens,
I ended up on fGW services both ways, but PAYG is also valid on Heathrow
Connect as far as West Drayton.

Three weeks earlier, business took me to South Greenford, where my Oyster
PAYG was also accepted.

Chris