Hi, problem with my glow worm 30ci boiler:the water temperature fluctuates from hot to cold ,back to hot to cold etc. When I open a hot water tap, I can hear the burners ignite but the water only gets luke warm, then I hear more burners ignite and the water gets hot but only for a few seconds before returning to only luke warm.The boiler then ignites again to give me a few more seconds of hot water before returning to luke warm, then ignites again to give me a few more seconds of hot water and so on. The boiler doesn't switch off while the water is flowing , so I presume there are 2 sets of burners. I had this problem fixed under guarantee once before. The repairer hadn't got a clue as to the fault and replaced almost every part in the boiler before the fault was rectified and he didn't know which part cured the fault. Thus, I don't want to go down this road again, now that it is out of warrranty. The boiler is 4 years old. Any ideas

Will, July 2007

Hi, Thanks you were right, it was a sludged up heat exchanger. Flushed with Sentinel x 400 which solved the problem. Thanks!
Will

Will, August 2007

try descaling the plate heat exchanger first,if it scaled up the the water flow throw it is resticted so the water gets to hot and turns off the burner then when it runs cold again it will re-ignite

paul, July 2007