boiler topup

Hi folks, Im having problems topping up my boiler. I have read some of the other posts on the forum and thought I found the loop on the boiler but pressure wont shift. Here are the pipes, I am actually in italy. Not sure if that is the issue and pipes are set up different. But definitely cant...

I have a Worchester Bosch Greenstar 25Si Compact Combi Bolier. In generally works fine however sometimes it needs topping up. To do this there is a little blue leaver on the bottom of the bolier. Recently this lever has got very stiff I am almost worried if I pull it down to hard it will snap...