Quick question - is the yellow middle of the inside of the cap supposed to move at all? I seem to remember reading it should move in and out to release pressure but can't remember and can't find the info now.
Cheers guys and ladies

I dunno exactly if the middle will move or not cos the valve might be beyond it but the cap must work as to keep 1.4bar pressure in the system... i have a spare in the boot, i'll check it tomorrow then confirm