Baxi Combi 105e Pressure problem desperate for help!?

Hello, I have a baxi combi boiler 105e and the pressure was completly off the scale well over 4bar. I released water from bleeding the rads and got it down to around 1 bar. After turning system back on after a few minutes the pressure went straight back up to full again!!! So I tried again and this time took enough water from rads to get the pressure to read 0bar (ha ha i thought to my boiler! got you this time) But no :0( episode 4 revenge of the baxi ! it went straight back round to full? when it is powered on the overflow outside is spewing hot water??? Please help can't afford a plumber this close to christmas and it's getting cold!! Thanks Guys.