How can I repressurise my Volkera combi boiler?

I have a Vokera excell 80sp combi boiler and the water pressure gauge has dropped into the red. Because of this it is not firing when the hot taps are turned on, and we have no hot water unless we have the heating on aswell.
The water coming into the flat has not changed noticably in pressure, and none of the other flats are having this problem. We have been advised by friends that combi boilers need to be repressurised every now and then and they turn a little dial thing on theirs. However, we cannot see how to do this on ours and there is nothing related in our users instructions manual. Would someone be able to help us please?