Within these instructions it details the pressure gauge is in the lower boiler housing. Below the boiler there are two taps (as you said below) One of these taps is the quarter turn tap and this should be to allow water into the system to increase pressure.
As you open the tap slowley the pressure should increase and set to 1.5-2 bar.
These taps can get stuck and altough the lever turns it does not open the valve- this might be the problem as it appears you have already tried this already.
A word with the plumber friend!
Maurice
November 2010