Quick answer
A toilet that keeps running usually has a faulty flush valve seal, float or fill valve, allowing water to pass into the pan or overflow. If the cistern has an accessible isolation valve, turn it off while arranging a repair.
Check where the water is going
Remove the cistern lid carefully if it lifts off; some lids are attached to push-button fittings and need a specific release. Do not force it. Listen for a constant refill and look for water running into the toilet pan or reaching the overflow. A small amount of food colouring in the cistern can help reveal water passing into the pan; do not flush during the check.
If water is escaping onto the floor, stop using the toilet and close its isolation valve if you can reach it safely. Wipe up water and keep it away from electrical equipment. A leak from a concealed cistern may require access by a plumber.
Common cistern faults
- A worn flush valve seal may let cistern water seep into the pan, triggering repeated refilling.
- A float set too high or obstructed can cause the fill valve to keep admitting water.
- A faulty fill valve may fail to close even when the float rises.
- A misaligned flush button, chain or linkage may hold the flush valve open.
Safe checks and repair
- 1Find the small isolation valve on the supply pipe to the cistern. Turn it gently clockwise, if it moves freely, then flush once to lower the water level. Do not force a seized valve.
- 2With the water isolated, check that a visible float moves freely and is not caught against the cistern wall. Look for an obviously displaced chain or button linkage.
- 3Only adjust or replace parts if you understand the cistern design and can restore it correctly. Shut off water first, and follow the maker's instructions for the exact model.
- 4Turn the supply back on gradually and watch the cistern refill. Check that the fill stops and that no water reaches the overflow or floor.
Avoid repeat problems
Do not put toilet cleaning blocks inside the cistern unless the cistern maker approves them; chemicals can damage seals. If the toilet is still running after a basic check, the correct seal or valve may need fitting. TraceFix can investigate persistent toilet faults and leaks in Birmingham and London.
When to call a plumber
- The isolation valve is seized, leaking or inaccessible.
- Water is escaping onto the floor or from a concealed cistern.
- The toilet continues to refill after a visible obstruction is cleared.
- You are unsure how to remove or refit the cistern lid or flush mechanism.