Isolate the radiator - not the boiler.
They have two valves - inlet and outlet and a bleed screw.
Turn both valves off - isolating the radiator - put something down to protect the floor and to catch the water - it will probably be very black. I usually use a paint-roller tray to catch the water.
Slightly undo the connection between valve and radiator - and slightly loosen the bleed screw at the top to let air enter the radiator so that water can flow out.
Have a bucket handy to put the dirty water in - you can control the outflow by adjusting the connection and the bleed screw - finally loosen the other radiator valve - LEAVING BOTH VALVES ON THE PIPES - not on the radiator.
Lift the radiator upwards and remove from the wall - take care - there will still be black water ready to leak out on the floor. Sometimes it's best to close the bleed screw and carry the radiator upside down.
Alternatively hire a plumber and watch what happens.
Good Luck..., August 2015
