Why a toilet runs on
Two valves do the work: the flush valve at the bottom lets water out when you flush and should seal afterwards; the fill valve refills the cistern and should shut off at the right level. If either fails, water keeps moving — and keeps running.
Flush valve or fill valve?
If water is trickling into the pan constantly, the flush valve (or its flapper/seal) isn’t sealing. If the cistern overfills and drains through the overflow, the fill valve isn’t shutting off. A little food colouring in the cistern — if colour appears in the pan without flushing — confirms a leaking flush valve.
Quick checks
Lift the lid and look: is the water sitting above the overflow line? Is the float set too high? Is the flapper/seal worn or misseated? Sometimes it’s just grit holding a valve open. Often, though, a perished seal needs replacing.
When to call a plumber
If a clean and a re-seat don’t stop it, the valve needs replacing with the right part for your cistern — and that’s where a plumber saves you a frustrating afternoon and a second trip to the merchant.
Toilet still running after a look inside the cistern? We’ll swap the faulty valve for the right part and stop the waste. Local, Gas Safe, no hard sell.
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