After about 5 years of trouble free heating my boiler has suddenly developed a problem. On gravity hot water it overheats and does not shut off in time before the water starts to boil. I have changed both the thermister and the overheat sensor and have checked out the cyltrol valve fitted to the cylinder. Any ideas please.

Ray, September 2009

Ray, Did you ever solve the problem? Our 5 year old Kingfisher has started doing exactly the same. The header tank is full and have bled the system recently to eliminate any air. I have also noticed that as it switches off the internal relay clicks many times after the burner has gone out, as though it is trying to start again.

Eleman, February 2010

May be a silly question, but have you checked the water level in the Feed and Expansion cistern in the loft, if the Ball valve is stuck, the system may be short on water, causing excessive residual heat build up leading to the boiler overheating

www.elanar.co.uk, September 2009