Toilet won't flush or has a weak flush

✅Free DIY guide — no sign-up required. Written by a qualified Gas Safe engineer.

DIY Friendly💷 £0–£30⏱ 15–40 min

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Most likely cause & what to check

Remove the cistern lid and check if the flushing mechanism is connected — the chain or lift arm sometimes detaches.

Check the water level — it should sit 25mm below the overflow pipe.

For older siphon cisterns: the rubber diaphragm has perished — a replacement kit costs around £3.

For modern push-button cisterns: the flush valve seal is likely worn — replacement kits are available.

Replacement siphon or flush valve

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