A toilet that keeps running after flushing can waste a surprising amount of water and usually indicates that something inside the cistern is not sealing or shutting off correctly.
Modern push-button toilets and older lever toilets use different mechanisms, but the basic principle is similar: the cistern fills to a set level and should then stop.
After flushing, the cistern should refill and then the incoming water should stop. If it continues running, either the fill mechanism is not shutting off or water is escaping into the bowl and causing the cistern to keep refilling.
The fill valve controls incoming water. A float moves with the water level and tells the valve when the cistern is full.
Problems can include a float catching on another component, incorrect adjustment, a worn fill valve, limescale, debris or a damaged seal. If the float cannot rise freely, the water may continue running.
A flush valve opens when the toilet is flushed and should then reseal. If the seal is worn or contaminated, water can slowly leak from the cistern into the bowl.
The fill valve then repeatedly replaces that lost water. Signs include a constant trickle into the bowl, the cistern refilling periodically or water movement long after flushing.
The cistern water level should remain below the overflow. If the fill valve is adjusted too high, water may continuously escape through the overflow system.
Many modern toilets use a push button connected to the flush valve. If the button sticks or the cable is incorrectly adjusted, the flush valve may remain slightly open.
Check whether the button returns fully after flushing.
Observe the water surface in the bowl after the cistern has finished filling. Look for ripples, a thin continuous stream or water movement at the back of the bowl.
A food-colouring test can also help on suitable toilets. Add a small amount of colouring to the cistern water and wait without flushing. If coloured water appears in the bowl, the flush seal is likely allowing water through.
Listen after flushing, check the button or handle, look at the float if safely accessible and check whether the water level rises excessively.
If the toilet has an accessible isolation valve and is running continuously, turning off its water supply can prevent waste until it is repaired. Do not force a seized valve.
A toilet that occasionally refills even though nobody has flushed it often has a slow leak from the cistern into the bowl. As the water level falls, the fill valve opens briefly to replace it.
Yes. A continuous or frequent leak can waste a considerable amount of water over time, particularly in metered properties.
Professional help is sensible when the toilet continuously runs, the cistern overflows, internal parts are damaged, the isolation valve leaks, push-button mechanisms are difficult to access or the toilet keeps refilling by itself.
TES Heating can diagnose and repair toilet cistern, fill-valve and flush problems across London.
Repair slow leaks early, do not force flush buttons or handles, address limescale build-up and replace worn seals when required.
A fill valve may not be shutting off or the flush valve may be leaking water into the bowl.
A slow cistern-to-bowl leak can lower the water level and trigger the fill valve again.
If there is a working isolation valve serving the toilet, you may be able to turn off the water supply until repair. Do not force a seized valve.
It is not usually an emergency if water remains contained, but it should be repaired promptly to avoid water waste or overflow.
Yes. Deposits can interfere with valves, seals and moving components inside the cistern.
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