have changed 3 way valve problem with no ch, this now works but pressure rising above 3 bar if boiler is used on full temp temp left at half it stays at 2.5 bar?
You will find that the expansion vessel has lost it charge. You can repressurise by using a foot pump up to 1 bar of pressure and make sure that the system has no pressure in it otherwise it will give you false readings and its normally sited at the back of the boiler
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix home heating systems.