Chaffoteaux Britony 80 Combi - Heating Problem

My Chaffoteaux Britony 80 Combi has developed a fault - The DHW seems to be running ok - but when the tap is turned off the boiler carries on running - thus not switching back to CH. I have found that if I turn the tap on and off (about 30 times sometimes) the boiler will then stop and switch over to CH. While in DHW mode with the tap off it does stop firing but something still running, then about a minute later it will fire for 10 seconds (keeps going on like this ) ?? Im hoping its not the 3 way valve as this was only fitted just over a year ago!!. Any ideas gratefully received. Thanks in advance.

sounds like a sticking flow switch, they tend to stick on that model of boiler, when its take apart it looks like a car engine valve with a magnet on top, it activates a reed switch, think it the one on the right hand side, pull of the wire and see if it still carrys on running on

allow me to correct myself its on the left! the one on the right is for the heating, look in the book think they call it a domestic hot water throttle, it looks like a black screw on bottle top. Easy change if it is, you would need to turn the water of first and make sure you dont get the wrong one or you will get a free shower