Toilet not flushing properly — weak or incomplete flush

Check the water level in the cistern: lift the lid and look inside. The water level should be about 25mm below the overflow tube. If it's too low, the flush won't have enough force. Adjust the float arm or fill valve to raise the water level.

For close-coupled or wall-hung toilets with a flapper valve: the flapper (rubber disc) at the bottom of the cistern lifts when you flush. If the flapper is worn or warped, it won't seal properly between flushes AND won't fully open when flushing, reducing flush power. Replace it (under £10, easy DIY).

For older UK toilets with a siphon: the siphon mechanism lifts an upturned U-tube to create the flushing action. The plastic diaphragm inside can perish. Replacement siphons are about £8–£15 — turn off the water, drain the cistern, and swap the unit.

Check the flush pipe (the pipe from the cistern to the pan on older WCs) is clear and not partially blocked with limescale.

For close-coupled toilets, check the rim holes under the toilet bowl rim are clear — limescale blocks these jets over time, reducing flushing efficiency. Use a descaler and a bent wire to clear them.

Check the waste trap and soil pipe are not partially blocked — a partial blockage downstream of the toilet reduces flush effectiveness even when the cistern is fine.

If the toilet is dual flush, the flush button mechanism may have become disconnected from the valve inside the cistern. Inspect inside and reconnect the linkage if needed.