The cister will not flush?

I have a grohe push button Cistern which is 16 months old. Up to yesterday it worked fine then no flush when pressed. Having removed stripped and examined the mechanism/bellows etc it is quite clear everything is in order except the bellows are not compressed suggesting the central valve is not ring to its limit which it is. the plastic bellows cannot be adjusted which convinces me there is some sort ofpart missing between the end of the bellows and the tube if this was the case the flush would work. I cannot get hold of a diagram to confirm. Can you help or confirm.

Thank you