I have a LAB toilet cistern has been overflowing into pan. It fills up but the water does not stop so it goes down the overflow pip in centre and into toilet. The Blue Screw within the white Flush valve assembly changes the amount of water in the short flush. The White overflow in the middle in the picture is adjustable but all it changes is how high the water fills. I need to know what to replace or how to fix. It seems to me that the white screw within the Blue fill valve assembly should be allowing me to adjust at what point the water coming in cuts off or perhaps the speed of the water input, but it does not seem to work. even if I lift it manually the water still fills and goes down the overflow pipe in the centre of the picture. So looking at the picture should I replace the White Flush valve assembly (LAB B206/B220) on the left of the pic or the Blue fill valve (LAB A207) on right of pic? The White part is easy, does not even require water off, it is just a bayonet and a simple twist it can be removed. I checked under and there does not seem to be any dirt or mess. The blue part seems more complicated, especially as whoever installed this put the pipe behind a tile enclosure so I will have to turn off main supply at main. Does the blue cap on top come off easily, is there anything in there that would be servicable?