Toilet keeps running? Quick fixes for cistern faults

A toilet that keeps running after flushing is usually suffering from a cistern fault rather than a problem with the pan itself. The water may trickle continuously into the pan, refill at intervals, make a loud noise while filling or rise towards the overflow.

Most homeowners can carry out a few safe checks before calling a plumber. The key is to identify whether water is escaping through the flush valve into the pan or entering the overflow because the fill valve has not shut correctly.

Identify your cistern type and main parts

Modern toilets commonly have a push-button dual-flush cistern. These use two buttons for a smaller or larger flush, with a flush valve or siphon beneath the lid. Older toilets often have a handle or lever on the side, connected to a traditional siphon or flush valve by a chain, rod or linkage.

Although designs vary, the important parts are similar. The fill valve admits fresh water, the float measures the water level, and the flush valve or siphon releases water into the pan. The overflow prevents the cistern from filling beyond a safe level, either through a separate tube or directly through the flush valve.

Start with safe checks

Remove the cistern lid carefully and flush the toilet once while watching the mechanism. Keep fingers clear of moving parts, and do not force a button, lever or valve. If water is flowing continuously, locate the small isolation valve on the pipe supplying the cistern and turn it clockwise to stop the water temporarily.

• Check whether the water level is reaching the overflow opening or tube.

• Look for water running steadily into the pan from beneath the flush valve.

• Gently lift the float to see whether the fill valve stops admitting water.

• Check that the float, arm, chain or push-button mechanism is not rubbing against the cistern.

If the water stops when the float is lifted, the float may be stuck, incorrectly adjusted or damaged. A float should move freely without catching on the cistern wall or other components. On some older valve designs, the water level can be adjusted by turning a screw or gently repositioning the float arm, but avoid bending parts forcefully.

Check the water level and overflow

The water should normally sit below the overflow level, often around 20 to 25mm below the top of the internal overflow tube. If it is too high, water will continuously pass into the overflow and down into the pan. Lowering the float setting slightly may solve the problem if the fill valve is otherwise working correctly.

If the fill valve does not stop even when the float is raised, the valve may have a worn diaphragm, washer or internal seal. You can turn off the isolation valve, remove the valve cover where accessible and clean away grit or limescale, but only dismantle it if the design allows this safely. A damaged diaphragm or washer usually needs a like-for-like replacement, and the water supply should remain isolated during the work.

Find out whether water is running into the pan

A cistern can have a normal water level while still allowing water to run into the pan. This usually points to a worn, dirty or poorly seated flush valve seal, or to a siphon that is not returning fully after the flush. Press the flush button or lift the lever gently and release it. If the running changes when you operate the control, the flush mechanism may be sticking.

Mineral deposits around the seal can sometimes be cleaned carefully with a soft cloth, provided the water is turned off first. Do not use excessive force or sharp tools, as a scratched sealing surface can make the fault worse. If the rubber seal is cracked, distorted or no longer seats evenly, replacing the seal or the complete flush valve may be more reliable.

Match the symptom to the likely fault

Intermittent refilling often means the flush valve seal is allowing a small amount of water into the pan. As the level drops, the fill valve briefly opens to top the cistern back up. A toilet that is noisy during refill may have a partially closed isolation valve, restricted inlet filter, limescale or a worn fill valve.

If water never stops, first confirm that the float is free and that the water is not reaching the overflow. If raising the float makes no difference, isolate the supply and arrange a replacement fill valve or internal washer. Never leave a cistern running unattended, as it wastes water and can eventually cause damage around the toilet.

Know when to call for plumbing repairs

DIY checks are suitable for identifying straightforward adjustments, but replacement parts need to be fitted correctly to prevent further leaks. Contact Robert Hill & Co Ltd for plumbing repair if the flush valve, siphon or fill valve needs replacing, or if you cannot identify the source of the running water.

Professional help is also advisable if the local isolation valve or household stopcock is seized, damaged or will not shut off the supply. Call 01419562245 to arrange assistance and get your toilet cistern operating quietly and reliably again.