A toilet usually keeps running after flushing because water is slipping past a worn seal into the pan, or because the cistern is not shutting off its supply once it is full. Thames Water says leaky loos are usually caused by a faulty flush valve or fill valve, though the exact part can only be confirmed by checking the cistern.
A running toilet can waste a surprising amount of water, so it is worth sorting out even if it seems minor.
How to Tell If Your Toilet Is Running
Sometimes you can hear a faint hiss or trickle long after the flush. Other times it is silent. You may see a thin ripple of water running down the back of the pan, or the cistern may refill on its own every so often without anyone using it.
Thames Water suggests a simple check. Dry the back of the pan, then place a sheet of dry toilet paper there and leave it for at least three hours without flushing. If the paper is wet or torn, water may be leaking from the cistern into the pan.
Common Reasons a Toilet Keeps Running
Many modern toilets use a flush valve with a rubber seal at the bottom of the cistern. If the seal is worn, dirty or slightly out of place, water can seep past it. Limescale and debris can stop it sealing properly.
The fill valve controls water coming into the cistern. If it does not shut off at the right level, water may keep entering and run away through the internal overflow into the pan. A float set too high can do the same.
Older toilets with a syphon and lever may have a worn diaphragm, which can cause problems with flushing as well as running. Each design behaves a little differently, so one symptom does not prove which part has failed.
What You Can Safely Check
Lift the cistern lid and look inside, without taking anything apart. Check whether the water level is close to the overflow tube or marked line, and whether anything such as a chain or loose part is caught under the valve.
If water is escaping from a pipe outside the property instead of into the pan, that is an overflow issue and may need a different approach.
Do not force stiff valves or dismantle parts connected to the mains water supply. If the water needs to be stopped, use the isolation valve on the toilet supply pipe only if it turns easily.
Getting It Fixed
Most running toilets can be put right by replacing or adjusting the faulty part rather than the whole toilet. The right part depends on the make and type of cistern, so it helps to know whether you have a push button or a lever flush.
If your toilet will not stop running, our toilet repair service in Oxford can check the cistern and replace the worn part, so you are not paying for water you never use.