Bigal wrote:

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 ?

Only that if you let out too much water, you may lose a little pressure
and need to top up afterwards. See the sealed system FAQ if you need
details on how to do that:

http://www.makewrite.demon.co.uk/SealedCH.html

--
Cheers,

John.

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