A toilet usually keeps running after flushing because water is either leaking from the cistern into the pan past a worn seal, or the fill valve is not shutting off when the cistern is full. Several parts can cause similar symptoms, so the exact fault usually needs checking.
A running toilet can waste a lot of water over time, and may push up your bill if you have a water meter. It is usually worth fixing sooner rather than later, even if the noise does not bother you.
Water Trickling Into the Pan
Many modern cisterns use a flush valve with a rubber seal at the bottom. If that seal is worn, dirty or not seating properly, water can slowly escape into the pan. The cistern then keeps refilling to replace it.
A simple way to spot this is to look at the back of the pan a while after flushing. Water still moving there, when the cistern should be full and quiet, suggests water is getting past the valve.
You may see a thin trickle of water running down the back of the pan, or hear the cistern refilling every so often when no one has flushed. Older toilets with a siphon can have similar problems if parts inside wear.
The Cistern Not Stopping When Full
The fill valve lets water into the cistern and should shut off once the water reaches the right level. If the valve is worn, the float is set too high, or debris is stopping it closing, water may keep coming in.
Many modern cisterns have an overflow inside that sends extra water into the pan. Older cisterns may have an overflow pipe that runs outside, so the first sign may be water dripping from a small pipe on an outside wall.
Constant running does not always mean one particular part has failed. The same symptoms can come from the flush valve, fill valve, float or overflow.
What You Can Check
Lifting the cistern lid carefully and looking at the water level can give a clue. If water is running into the overflow, the cistern may be overfilling. If the level is normal but the cistern keeps refilling, the flush valve seal may be letting water through.
If the toilet has an isolating valve on its supply pipe and it turns easily, closing it can stop the running while you arrange a repair. Do not force it if it is stiff.
Getting It Repaired
Parts inside cisterns vary between makes and models, and some are not easy to swap. A plumber can check which part is causing the problem and whether it can be adjusted, repaired or replaced. Our page on toilet repair in Poole explains common toilet faults and how they are repaired.
If your toilet keeps running at your Poole home or business, a plumber can find the cause and explain the repair options.