there should be a drain valve on the rad furthest away from the boiler or just on the ground floor, have all your rad valves open on the other rads, connect a hose to the drain valve & open & just let the water run away until it stops, there should be a pressure relief valve on the boiler which you can turn until you hear water running away & see the pressure gauge drop, this will drain the boiler very quickly, if no drain valve then you will have have to drain each rad in turn
bamba
October 2009