Thanks for those tips. It happens on all the taps its just more noticeable when getting a blast of cold water first thing in the morning in the shower. Will try the filters and sensor etc on the boiler.
system is 3 years old in small house, boiler in downstair kitchen. When using shower in bathroom upstairs the water gets hot and then cools after a minute or two before getting hot again. This then continues for as long as you like. When listening to the boiler it sounds like it is constantly firing...
