Baxi Combi 105 HE Pressure Gauge Fault?

Hi, can anyone advise ... i can't seem to get my boiler to maintain a 'normal operating pressure' - i noticed yesterday the gauge had risen to nearly 4 bar and have tired bleeding one of my rads to reduce the pressure - which works temporarily and then it just rises back up again. Its been working fine and only 11 months old; do have warranty but baxi's offices are closed and can't get hold of my plumber :o( would be great if someone could help me as scared to switch heating on and it's really cold :o((( Thanks in advance!