A toilet that keeps trickling water into the bowl can waste a surprising amount of water — and if you are on a meter, you are paying for every litre. The good news is that the cause is almost always one of two parts inside the cistern.
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Written by Chris Gill, C Gill & Son Plumbing & Heating ·
What 'running' actually means
A running toilet is one where water keeps moving after the flush has finished. Sometimes you can hear it — a faint hiss or trickle. Sometimes the first sign is a rippling in the bowl or a damp patch on the back of the pan where water has run down. On a water meter, the dial creeping round with every tap off is the giveaway.
The cistern has two jobs: let water in to the right level, then hold it until you flush. A running toilet means one of those two jobs is failing, so water is escaping into the bowl or the overflow.
Cause one: the flush valve seal
The flush valve is the outlet at the bottom of the cistern. When you flush, a seal lifts and the water rushes into the bowl; when it drops back, the seal should sit watertight. If that seal is perished, warped or has grit under it, water trickles constantly into the bowl.
The test is simple: put a few drops of food colouring in the cistern water and wait fifteen minutes without flushing. If colour appears in the bowl, the flush seal is leaking. Cleaning the seal and the seat it sits on sometimes cures it; otherwise the seal or the whole flush mechanism needs replacing.
Cause two: the fill valve
The fill valve lets water back in after a flush and shuts off when the cistern reaches the right level, usually via a float. If the valve is worn or the float is set too high, the water level creeps up until it spills down the overflow pipe — which on most modern toilets runs into the bowl, so it looks like the same fault.
Check the water level in the cistern: it should sit about an inch below the top of the overflow pipe. If it is level with it, the fill valve is not shutting off. Some floats can be adjusted down with a screw; if the valve itself is worn, it is replaced as a unit.
Is it worth fixing yourself?
Both parts are cheap and, on many modern cisterns, designed to be swapped without tools. If you are confident turning the water off, emptying the cistern and following the instructions that come with the part, it is a reasonable DIY job. The fiddly part is usually identifying exactly which valve your cistern uses, as they are not all interchangeable.
Where people come unstuck is over-tightening plastic fittings, cracking the cistern, or discovering the close-coupled bolts between cistern and pan have corroded solid. If any of that sounds familiar, it is a short visit for us.
When it is more than a running toilet
If the toilet is also slow to flush, the cistern is cracked, or the pan rocks on its fixings, the running water may be the least of it. Our toilet repair and installation page covers the wider faults, and if the toilet is old enough that parts are hard to find, replacement is often the better value.
Need it sorted? Book a toilet repair
Send a photo of the inside of the cistern on WhatsApp or use the quote form, and Chris will tell you what is likely needed. If you would rather talk it through, ring 07429 632804. Our toilet repair and installation service covers running toilets, leaks at the base and full replacements across Neath, Port Talbot and Swansea.
Covering Neath, Port Talbot, Swansea and the surrounding area.
Common questions
Toilet keeps running FAQs
Clear answers before you arrange a visit.
Why does my toilet keep running water?+
Almost always one of two parts: the flush valve seal letting water trickle into the bowl, or the fill valve not shutting off so water spills down the overflow. The food colouring test tells you which.
Does a running toilet waste much water?+
Yes. A steady trickle can waste hundreds of litres a day, which adds up quickly on a water meter. It is worth fixing promptly.
Can I fix a running toilet myself?+
Often, yes — the parts are cheap and many are designed for DIY replacement. The challenge is identifying the right valve for your cistern and not over-tightening plastic fittings.
Why does my toilet randomly start running at night?+
Usually a slow leak past the flush seal: the water level drops, the fill valve briefly opens to top it up, and you hear it in the quiet. The seal needs cleaning or replacing.
