You'll find that the system is probably full of sludge...if you want to have a go yourself, turn both radiator valves off - undo valves from the radiator (not from the pipes!!) and allow the rad. to drain down. Have a collecting bowl ready and turn one valve on at a time. If clear water runs freely then there isn't a blockage. When you're happy with this, reconnect the rad, open the valves and bleed in the usual way.
John
January 2008