A toilet cistern that keeps filling with water is usually losing water somewhere, or its fill valve is not shutting off properly. Common causes are a worn flush valve seal letting water seep into the pan, or a float set too high so water runs away down the overflow.
What “ghost flushing” sounds like
Some people notice the cistern starting to refill by itself at intervals, even when nobody has used the toilet. This is sometimes called ghost flushing. It often happens when water slowly escapes from the cistern into the pan. Once the level drops far enough, the float falls and the fill valve opens to top it up again.
A constant trickling refill is slightly different. Here the fill valve may never fully close, so a thin stream keeps running in.
Why the cistern keeps topping itself up
The fill valve is the part that lets fresh water into the cistern. It is controlled by a float, which rises with the water and shuts the valve off at the right level. If the float is set too high, or it sticks on its arm or rod, the valve can stay open. Grit and limescale inside the valve can also stop it sealing.
If the water level sits above the top of the overflow, the extra water simply drains away and the valve keeps feeding more in. This overflow may run into the pan or out through a pipe on an outside wall.
The other common cause is the flush valve seal at the bottom of the cistern. When this rubber washer wears or gets grit under it, water slips past into the bowl. You may see faint ripples running down the back of the pan. This slow loss is what makes the fill valve wake up and refill every so often.
Checking for a leak and wasted water
WaterSafe suggests a simple toilet paper test for a leaky loo. Dry the back of the pan and lay a sheet of toilet paper across it. If the paper gets wet before you flush, water is likely trickling through from the cistern.
If your home has a water meter, a cistern that refills on its own can quietly push up your usage. A small, steady leak runs day and night. You could also lift the lid and see whether the water is close to or above the overflow. Try not to bend the float arm or force parts, as plastic fittings can snap.
When a plumber should investigate
It makes sense to get help if the cistern keeps refilling after simple checks, if the overflow is running outside, or if parts look cracked or heavily scaled. A plumber can check the fill valve, float setting and flush valve seal together, as one fault can hide another. Our cistern repair service covers faults like constant refilling and worn internal parts. Sometimes a new seal is enough, while older valves may be better replaced.
If your toilet cistern keeps filling and you live in or around Swindon, Emergency Plumber Swindon can take a look and talk you through the options. Call us on 01793 569521.