In message , John
writes
My 1988 house has the C/H pipes behind the plasterboard. I have a concern
that one radiator is not getting hot and have discovered a restricted flow
from one of the pipes. (8mm)

Check the TRV before engaging in major surgery. I have two *sticky* ones
in a 15 year old installation. Top unscrews to reveal a small plunger.
One day, I am going to ask in here if any sort of lubrication is likely
to help:-)

regards

--
Tim Lamb