A dual flush gives two volumes from one cistern, usually around 3 and 6 litres, and on most modern flush valves both are adjustable. The adjustment is part of fitting the valve, not a hidden setting.
How the two volumes are produced
The valve opens to a different height, or closes at a different point, depending on which button is pressed. The full flush lets the cistern empty; the reduced flush closes early.
Where the adjustment is
On the valve body, usually a sliding clip or a screw collar that sets how far the float travels. The manufacturer’s instructions describe it for that model — it varies enough between makers that a general description would be wrong.
Why you might want to change it
A pan that needs two flushes is using more water than a single correctly set full flush. Adjusting up is as legitimate as adjusting down, and it is the honest answer when a “water-saving” setting is not clearing the pan.
What the volume actually depends on
The cistern, the valve setting, and the pan. The same valve at the same setting in a different cistern delivers a different volume, which is why the figure is quoted for a combination rather than for a part.
Questions people actually ask
Are the buttons standard between makers?
The plates are not. A flush plate is matched to the valve and the frame behind it, and swapping brands usually means changing the valve too. That is worth knowing before buying a plate for its looks.
Why does my reduced flush not clear the pan?
Either the volume is set too low for that pan, or the pan itself needs more. Adjusting the reduced volume upwards is the first thing to try, and it is described in the valve's instructions.
Last reviewed 5 September 2026