Ariston DIA boiler keeps losing pressure

[lambrett]

Hi all i have an Ariston DIA combination boiler which keeps losing water pressure every time you switch it off, the pressure goes back to 0.0 bar.There are no apparent leaks on the system but the overflow pipe sometimes not always discharges water. This is only when the Central Heating is on, I have to pressurize it back to 1.0bar for it to work again, All help Appreciated

 

[twgas]

expansion vessel probably needs recharging, see FAQs. PRV will more than likely need replacing as well.