hi yes the expansion vessel either needs filing with air or replacing its normally a red tank round or oval check the online manuals to see pics of it. u can pressure rise by draining the system of water to 0 bars then putting a car air pump to the valve and filling it to 2 or 3 bar pressure. after this refil the system if the problem reoccurs in the future then the vessel is leaking and will need replacing
kash, September 2012
