I have a problem with a worcester bosch 30si boiler. When i put the central heating on, it comes on ok for about 4 mins, then it starts running faster and the pressure dial rises rapidly from 1 bar to 2 bar and then gets louder and cuts out. The green flame indicator is off and the pump and fan stop. It takes about 30mins for the pressure to drop enough for it to reset. The hot water from the taps work ok, until all this happens with the heating. Then I have to reset the boiler before I get hot water again. I hope someone here can help me please.