worchester 240, pressure dial reads same hot or cold?

my worchester bosch 240, works fine, but for the pressure dial does not move from 2.9 weather central heating/water is on full and hot or off and cold , a trickle of water is expelled out side. tried red knob pressure release to bring it down , but goes back to same point and stays there all the time . tried also replacing regulator valve at the loop .