How do you raise the pressure on a Alpha 240e Boiler?

I have the above boiler and I can not see where to fill the pressure, due to the gauge being on 0. I have found the wire mesh cable where I thought the key or screw would be to raise the pressure but there is no key or screw at the end of the wire gauge.

Do you have any pictures of where the pressure filler tap or screw would be ?

Regards

K Rowe