boiler worcester 400 vessel bar pressure fluctuates?

hi my computer been down anyway now fixed bolier not pressure seems to go up and down bar between 1 and 4 and water comes out of outside flow pipe and after a while put more water to increase bar again as too low .when i release water from radiator goes down to about 0.25 bar anybody help please
the expansion vessel has valve on side what should be recommended pressure using foot pump is should this be the answer thanks for any help steve
ps expansion vessel zenit 12 litre 3 bar on label thanks