Remarkable that I should need to be posting this at all, but the Roca toilet flush buttons are an absolute disgrace.
They need to be set up perfectly or else they’ll get stuck, and if they get stuck the toilet flushes permanently and the cistern will then never fill. A well-meaning guest will then attempt
to fix the buttons and in doing so break the cheap plastic tat. I would not buy Roca again for this reason.

The button comes in two chrome halves both of which sit atop a white plastic screw thread that regulates the height of the button compared to the chrome surround that they sit in.

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The chrome surround itself gets screwed to the flush mechanism by a black plastic screw. The chrome buttons cover this screw so if the buttons stick, heavy handed guests attempt to lift off the cistern cover and in doing so break this chrome surround.

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The trick is to get the two halves of the button set up correctly.
If the buttons are already in place you need to take then out temporarily.
To do this push and hold the round half down and whilst it’s down carefully lift the crescent section vertically up and out. You can then remove the round half.

When you reassemble you need to make sure that the round half sits high enough in relation to the crescent that it can’t be pushed down past the crescent. you can regulate the heights by turning the plastic stems clockwise to lower the button or vice versa.

If the round half pushes down too far then it will get stuck.