Hi can anyone help I have just fitted an external expansion tank to a back 105e instant combi but the new tank has a pressure of 1.5 bar and my system should be around 0.9 bar it is an 8ltr tank should I reduce the pressure in the new tank to 0.9 bar at the moment it holds pressure when dhw is in use but as soon as CH is on the pressure builds up in the system and prv opens at around 2.5 bar is it the extra pressure in the new tank that is causing problem or do I have another fault in the heat exchanger blocked plate heat exchanger seems okay good dhw flow.
Graham[/b]
Graham[/b]