It wont switch off?

My boiler does not seem to cut out when the room has got to temperature, the thermostat is fine as it was working other day. This has happened before but though it might be the cold. However the pressure has risen to nearly 3 where it was set at below 2. Please does anyone have a suggestion as Im having to turn off at the mains at present :(

Julie Braithwaite
January 2010