Hey all, I've searched but I can't find an answer.
I can see that the Heathrow Express won't be running over the holidays for track work.
"24 - 29 December 2016: No service due to Network Rail improvement work
Due to planned Network Rail improvement work there will be no Heathrow Express services from 24 December to 29 December 2016.
A free Terminal Transfer service will run between all Heathrow terminals on these days.
Please check our website and Twitter feed (@heathrowexpress) for the latest service updates."

Will this track work also affect the Tube service to Heathrow?

I have a 12 hour layover on Dec 27, arriving terminal 5, departing terminal 3, with Heathrow Express down I'll be relying on the tube for the day to get out of the airport!

Thanks!