When the Toilet Cistern Won't Stop Filling: What's Really Going On?

 A toilet that won't stop filling isn't just annoying—it's a waste of water that can silently increase your water bill and signal deeper plumbing issues. If you've ever turned the handle or flushed the toilet a second time hoping to "fix" the problem, you're not alone. But a toilet cistern that constantly flushes usually means something inside isn't working as it should.

The most common culprit is the flapper valve, a rubber seal at the bottom of the cistern that rises when you flush and closes when the cistern empties. If the flapper valve is old, cracked, or warped, it doesn't seal properly, causing water to slowly leak into the bowl. As a result, the cistern keeps trying to fill, even though it's never truly empty.

Another common problem is the float mechanism, which controls the amount of water entering the cistern. If the float is set too high or becomes waterlogged, it won't close the fill valve in time. This can cause the overflow pipe to overflow, triggering a continuous filling cycle. Adjusting or replacing the float is usually a quick fix, but sometimes the entire fill valve assembly needs to be addressed.

Sometimes sediment or debris from hard water builds up around the fill valve, preventing it from closing properly. Especially in older toilets, components can corrode or harden due to mineral deposits, causing leaks and constant overflowing. In this case, replacing the valve is often more effective than trying to clean it.

In rare cases, the problem may stem from high water pressure or plumbing imbalances, which can put unnecessary stress on toilet components. If you've replaced components and the toilet still leaks, it might be time to call a plumber for a more thorough inspection.

Fixing a leaky toilet isn't just about convenience, it's also about savings and costs. Even a slow leak can waste hundreds of gallons of water a day. The good news? Most repairs are inexpensive, and catching the problem early can prevent long-term damage to both your plumbing and your wallet.

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