the problem was the domestic hot water diaphragm. pin holed. The diaphragm cost £8.50 from local boiler supplies. Heres how i did it. Turn off the 3 water valves ( cold supply, central heating in and out.)at the bottom of the boiler. switch off electrical supply. slacken the 2 screws that hold...
the kitchen sink is the last tap on the line and this is the main problem as i have to run upstairs to turn the sink tap on so the boiler will fire up, i can then turn it off and the boiler continues to run on 1 tap. if i put the shower on i turn the sink on for the boiler to fire up then its ok...