Why your toilet keeps running — and what it costs

You flush, the cistern refills, the house goes quiet — and then, a few minutes later, a short hiss as the tank tops itself up again. And again twenty minutes after that. Nobody calls a plumber for a hiss. But that hiss is a leak with excellent manners, and it is billing you around the clock.

The arithmetic nobody does

A modest cistern leak loses two to four litres an hour. Run that for a month and you have quietly flushed two to three thousand litres. A bad flapper can leak ten times that. Selangor's tiered water tariffs mean the waste lands in your most expensive consumption band — the litres you pay the top rate for. We have met running toilets that added RM30–RM60 to a monthly bill, every month, for a part that costs less than lunch.

The two-minute test

Take the cistern lid off and add a few drops of food colouring — or a spoon of Milo, we do not judge — to the tank water. Do not flush. Come back in fifteen minutes and look into the bowl. Colour in the bowl means water is escaping past the flush valve: confirmed leak. No colour, but the tank still refills periodically? The water is going out the overflow instead — different culprit, same waste.

The three usual culprits

1. A worn flapper or flush valve seal

The rubber seal at the bottom of the tank hardens and warps with age, letting water seep into the bowl continuously. This is the cause in well over half of cases, and the part is cheap. The catch: modern dual-flush mechanisms vary widely, and the wrong replacement seal leaks exactly like the old one did.

2. A misadjusted or failing float valve

If the float is set too high — or its valve no longer shuts off cleanly — the tank overfills and the excess runs down the overflow tube forever. Sometimes the fix is a simple adjustment screw. Sometimes the valve internals are worn and the whole inlet valve needs replacing.

3. A cracked overflow tube or flush assembly

Less common, but plastic assemblies do crack with age and over-tightening. Water escapes below the waterline where you cannot see it. If the flapper and float both check out, this is what is left.

When DIY stops making sense

Swapping an obvious, standard flapper is honest DIY territory and we cheer you on. Call a professional when the mechanism is a dual-flush unit you cannot identify, when the shut-off valve at the wall will not close (very common — they seize in the open position after years untouched), or when you have replaced the likely part and the hiss carries on. At that point, more parts-shopping usually costs more than our visit.

A running toilet is a fifteen-minute job for our plumbing leads, parts in the van, RM90–RM160 all-in for typical cases — and it pays for itself off your water bill within months. Book it alongside any other small job and the economics get even better.