Is your water main at 2 bar or above? This is an exerpt from the boiler installation manual.
• If the boiler loses water: the pressure will be indicated (a)
and the boiler ON indicator (b) will flash red indicating a fault.
Fill the system by the filling device (c) at the bottom of the boiler
until the pressure gauge reads 1.0 bar.
A mains inlet pressure of 2.0 bar is required to reach a fill
pressure of 1.0 bar.
TheBoilerMan
April 2010