Toilet keeps running: causes and fixes
A toilet that keeps running has one of two faults. Either the fill valve is not shutting off, so the water level rises to the overflow, or the flush valve seal is worn and water trickles into the pan. Lift the cistern lid: if the water is up at the overflow, it is the fill valve; if the level is normal but water still runs into the pan, it is the flush valve.
What the cistern is telling you
| Symptom | Most likely cause |
|---|---|
| Water level at or above the overflow | The fill valve is not shutting off |
| Level normal but water trickles into the pan | Worn flush valve seal or siphon washer |
| Dripping pipe on an outside wall | An external overflow fed by a failed fill valve |
| Cistern refills on its own every few minutes | A slow leak through the flush valve |
Stop a running toilet for now
- 1Find the isolating valveLook on the supply pipe to the cistern for a small valve with a slot.
- 2Turn it a quarter turnUse a flat screwdriver so the slot sits across the pipe.
- 3Flush onceEmpty the cistern so you can see whether water still enters.
- 4Book a repairA running toilet is usually a standard-hours job once the water is off.
Fill valve or flush valve?
Lift the cistern lid and look at the water level. If it is at or above the overflow tube or marked level, the fill valve is letting in too much water. If the level is normal but you can hear or see water running into the pan, the flush valve seal or siphon washer is letting it out.
Turning off just the toilet
Most toilets have an isolating valve on the supply pipe to the cistern, often with a small slot. A quarter turn with a flat screwdriver, so the slot sits across the pipe, stops water to the toilet without turning off the whole house.
Why it happens
Common causes:
- • Worn washer or diaphragm in the fill valve.
- • Float set too high, so the valve shuts off above the overflow.
- • Perished seal on a push-button flush valve, or a worn siphon washer on a lever flush.
- • Limescale on valve seats and seals, which is common on hard water.
Why it is worth fixing
A running toilet can waste a large amount of water each day, which matters if you are on a meter, and an external overflow dripping onto a wall causes damp. The repair is usually a replacement part inside the cistern rather than a new toilet.
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