I'm assuming you are referring to the removal of the radiators so you can plaster behind the rads.
You can do this one of two ways.
1. Drain the central heating system completely, if this isn't something you fancy doing probably best to give a plumber a call.
2. If you would rather do a specific room you could freeze the pipes, remove the rad and then cap of the existing pipes, agin if you don't feel confident doing this yourself best give a plumber a call. Hope this helps. Jason. JH Carpentry, Joinery & Building Services