you need to top up the  pressure to bar 1, the system you have is fill up by a tap  from the mains, there should be a tap or a lever , under the sink or near the boiler, when you turn on you will see the needle go from zero to bar 1,  you will need a friend to  help , to look at  the gauge as you very  turn the tap very slow, to  back fill ,  they will tell you when the gauge hits bar 1. and then you turn the tap off, and your done,  but open the tap very slow, you dont want to go over bar 1,
                 h
                
 January 2016