[SimonS]

It looks like it has been over pressurised.  These are supposed to be run with about 50/50 air to water in them.  I suspect that yours had very little air in it especially with your description of ‘tap on – pump on’.  On my B32 which uses the same bottle the pump does not come on until a few seconds after the tap is open and goes off a few seconds after the tap is closed. I have seen some instructions somewhere on what to do to maintain the correct ar/water ratio but cannot remember where at the moment!