I have a Vaillant Ecotec Pro 28. No water pressure?

I have the above boiler and this morning the heating didn't come on but the hot water is still coming through. The pressure gauge is below the grey area and the pressure is down to 0.6. I know i should 'top' the water up but i've been through all of the manuals and i've got a screw driver to the cold water inlet pipe underneath the boiler but there is no water going in and the manuals don't tell me how to do it or what i'm doing wrong.
Can anyone help please?