HI
The bleeding point on the heater hoses get blocked, Locate it with a haynes manual. If when you take the plug out when the engine is running and nothing comes out then try poking with a small screwdriver - gently. and dont burn yourself! do it when the engine is cold. Top up the collant level with some more water and hopefully thatl fix it. 
hope this helps
                
 jez
                
 April 2007