My central heating system is very noisy?
 
                I have a combi boiler which is about 5 years old.  When the heating comes on, I get a lot of clunking and clicking noises.  I have tried bleeding the radiators but it hasn't helped.  Can anyone tell me what to do please.  It's so noisy it's waking me up at night.
            
             Jo
            
 December 2011