ferroli modena

I’m staying at a friends & their boiler water pressure is scarily low at 0.1 bar! I can’t see how to top it up though & was hoping someone more capable than me may have an idea? The boiler is a Ferroli Modena 25S HE - I’ve attached a picture - the copper pipe to the left of the blue tap exits...

Hi, I'm looking for help advice please. The boiler pressure gauge was at zero, I tried re-filling/pressuring the system using the filling loop, but water started coming out the expansion vessel straight away. The vessel inner bag had burst! Replaced expansion vessel which was already set to 1...