bosche ICC2 combination boiler question

[ANDYG111]

Hi, I recently found that my ICC2 bosche boiler had lost all pressure. I turned it off, and tuned the tap on to fill it. the pressure needle went up to 0.5 bar and no further. As soon as I turned the tap off the needle went back down to zero !! Any advice greatly appreciated.

 

[vicvapour]

Was the boiler working previous to this pressure drop?

If so are there any obvious leaking from rads / valves?

If not it could be a "Under the floorboards and find the leak" jobby i'm afraid.