Does anyone have any idea or advice regarding my vaillant ecoTEC plus 630?

i have had all sorts of problems over the past 24 hours with my above named boiler. all the heating went off yesterday for no reason and upon checking the boiler it was even though off displaying a very high psi on they system 2.6 bar. Also it would ignite even though it tried i think four times then the error code 'F75' came up. The fault code changed a couple of times through the night but mostly displayed the F75 one but twice displayed 'S97'
i can get the boiler going but this involves bleeding one of the rads and then pressing reset button. i need to get the psi down to about 1.2 bar and then it will run for about an hour before its back at 2.6 or 2.7 at which time it turns off again. HELP