The message
from Peter Parry contains these words:

If ply was laid before tiles it is common to screw it down at about
12-24 in centres. I'd guess one or more (possibly all) of the screws
were too long and pierced the piping.

Seems odd to put ply down on top of UHF. Surely it'll insulate the floor.

--
Skipweasel
Pay no attention to that man behind the curtain.