In message . com, Bigal
writes
I want to loosen a radiator and turn it horizontal to apply wallpaper
behind it, are there any problems in doing this with a sealed,
pressurized system ?

It is, if the olive that connects the TRV to the 15mm pipe is faulty

.... still, I got a new carpet out of it !

Honestly - why do you need to turn it horizontally ? You just need to
move it away sufficiently from the wall to paper - the less movement,
the better

--
geoff