Check the water level
A flush needs a full cistern. If the water stops well below the mark, adjust the fill valve float upward — but keep it 20–25mm below the overflow.
Check the button and flush valve
- Press the button and watch: does the valve lift fully?
- Dual flush: the small button gives a short flush on purpose; check the large one.
- Adjust the button rods or cable length if the valve only lifts a little.
- A slow leak past the flush valve seal means a partly empty cistern — check with food colouring.
Limescale and rim holes
In hard water areas the holes under the rim can block. Turn off the water, flush, and scrub under the rim with limescale remover and a brush.
Partial blockage
If water rises high in the pan before slowly draining, something is partly blocking the outlet. Use a flanged plunger, or an auger.
Pro tip: Older large cisterns flush 9 litres; modern ones often 4–6 litres. Fitting a modern pan or valve without matching parts can give a weak flush.
