how do i bleed the radiators?

Use one of these...

http://www.toolstation.com/images/library/stock/webbig/59405.jpg

a radiator key - one side of the radiator at the top - undo the bleed valve half a turn or so to let the air out and hold a rag close to the escaping air - when water comes out tighten up.

Peccavi
January 2010