Our Ideal combi boiler is working well on central heating and hot water supply, until you turn the bath tap off. Immediately thereafter a series of loud creaking sounds can be heard in the boiler. This was noticed shortly after we had a new bathroom fitted and about the same time our heating was put into use for the winter. We have been through the book of heating engineers/plumbers with no success, all coming up with different ideas, saying they will get back to us, saying nothing is wrong etc etc. No one will even open it up. New bath taps and flexi piping were fitted with the new bathroom. We have checked with the manufacturers of the bath taps who say they are suitable for combi boilers. What could be wrong?