7 November 2026 · 1 min read · By the Plumbees team
If your cistern keeps refilling, you can hear trickling after a flush or you notice a thin stream of water running into the bowl, something inside is not sealing. It is rarely serious, but it should not be ignored. A constantly running toilet wastes water, and on a metered supply that shows up on your bill.
Common causes
- A worn flush valve seal or flapper that lets water leak slowly into the bowl
- A fill valve that does not shut off properly because it is worn or set too high
- A float that has become stuck or misaligned
- Limescale on the valve seat, common in hard water areas
- A cracked overflow tube or fitting
Simple checks
- Lift the cistern lid and look at the water level. If it is level with the overflow pipe, the fill valve is not closing.
- Gently adjust the float arm or float cup to see if the water stops at a lower level.
- Add a few drops of food colouring to the cistern. If colour appears in the bowl without flushing, the flush seal is leaking.
- Check that the flush handle is not catching and holding the valve open.
When to replace parts
Washers, seals and fill valves are inexpensive and are designed to be replaced. Replacing the mechanism is often quicker and more reliable than trying to repair old parts. If the cistern itself is cracked or obsolete, replacement is the better option.
When to call us
If a simple adjustment does not help, if you cannot find the cause, or if parts are hard to match, a plumber can diagnose and fix it in one visit. See our taps, toilets and showers service, or request a quote.