How to raise the pressure?

Please tell me how to increase the pressure to the appropriate level - it is currently below where it should be and the radiators won't work, although it still fires up and heats the water when the tap is turned on. Our old boiler had a small valve to twist and the pressure instantly increased. I left the valve open for a short time until the pressure had reached the required level, as indicated by the guage, when I closed the valve again. Very easy. I can see no such useful valve on the 532/i combi boiler. Please tell me where it is and how to use it.

Thanks