Thanks for the quick reply. Any recommendations on how to test this?
Do you by any chance know how this type of cistern is called? That might make it easier to find videos online.
The toilet doesn't stop filling up even if the water tank is full and keeps on overflowing the overflow pipe.
We've opened the toilet and the cistern looks like this. It's different from the ones I've seen on Youtube.
We've tried to adjust the height of the floating part by turning the screw...