The short answer
If a toilet keeps running, the cistern inlet valve, outlet (flush) valve, or a sticking button/float usually isn’t sealing. Lift the cistern lid only if it’s safe and you’re comfortable — sometimes a float is jammed. Don’t force parts or tip chemicals in. A running cistern can waste a large amount of water and, under Water Corporation’s rules, counts as a visible leak: it is not eligible for their leak allowance. Call McDermott Plumbing on (08) 6187 3999 or text 0406 882 648 to replace the valves or repair the cistern properly.
What’s going wrong inside the cistern
Modern dual-flush cisterns fill through an inlet valve and empty through an outlet valve in the base. Either valve can fail: the inlet won’t shut when the water hits the right level, or the outlet lets water seep into the bowl after the flush. Buttons and linkages can stick partly open. Older cisterns with ball-float arms have the same end result — water wasting into the pan or overflowing into the bowl.
- Inlet valve washer or diaphragm worn — cistern won’t stop filling
- Outlet valve seal warped or dirty — constant trickle into the bowl
- Button or cable stuck slightly depressed
- Float set wrong or fouling the cistern wall
- Hairline crack in an old cistern (less common — you’ll see water outside the toilet)
Quick checks (and what not to do)
- Listen at the cistern a few minutes after flushing. Ongoing hiss or refill means it isn’t sealing.
- Put a few drops of food colouring in the cistern water (not the bowl), wait without flushing: colour in the bowl means the outlet valve is leaking.
- If you lift the lid, don’t bend metal arms hard or overtighten plastic nuts — cisterns crack.
- You can turn off the small isolation tap on the water line to the cistern (if fitted) to stop the waste until a plumber arrives.
- Don’t use sealant tablets or drain chemicals as a “fix” for a running toilet — they don’t replace worn valves and can damage parts.
Water bills and Water Corporation leak allowance
Water Corporation’s public guidance treats leaks from toilet cisterns as visible, readily detectable leaks. Their leak allowance is aimed at hidden leaks (for example underground or in-wall pipework) that meet their eligibility rules — not a cistern that anyone can hear running. Fix the toilet early; don’t wait for a shock bill hoping for a rebate that won’t apply.
Their detect-a-leak material also notes that a running toilet cistern can waste a large volume of water over a year. The meter test on our leak detection page still helps: if the meter moves with every tap off, a running toilet is a prime suspect.
What we do on a running-toilet job
We diagnose inlet versus outlet versus button/float, replace the failed cistern internals with parts that suit your pan, and check the isolation tap and supply flex. If the cistern body is cracked or the suite is due for renewal, we’ll say so. Landlords and strata get an invoice that names the fault — useful when a tenant reports a “mystery” high bill.
We don’t publish prices on this page. You’ll know the scope before we start whenever the situation allows.
When it’s more than one toilet
If several toilets or wet areas are misbehaving, or the outdoor overflow relief gully is full, you may be dealing with a drain or sewer issue rather than a single cistern valve — see our blocked toilet and sewer responsibility pages, and call sooner rather than later.
Common questions
- Why does my toilet keep running after I flush?
- Usually the inlet valve, outlet valve or a sticking button/float in the cistern. The fill never stops, or water keeps leaking into the bowl. Call a plumber if a careful look doesn’t show an obvious jam. McDermott Plumbing: (08) 6187 3999 or text 0406 882 648.
- Can a running toilet increase my water bill?
- Yes. Water Corporation notes that a running cistern can waste a large amount of water over time. Fix it promptly — it’s one of the first things to check after a high bill.
- Does a running toilet qualify for Water Corporation’s leak allowance?
- No. Toilet cistern leaks are classed as visible, readily detectable leaks and are excluded from the leak allowance. Hidden pipe leaks are a different category — see our leak detection page.
- Can I stop a running toilet myself?
- You can turn off the cistern isolation tap if it has one, and you can check for a jammed float. Replacing inlet/outlet valves is a straightforward plumber’s job; if you’re not confident, don’t force plastic cistern parts.
- Is a running toilet the same as a blocked toilet?
- No. A running toilet wastes clean water into the pan. A blocked toilet won’t flush or backs up. Different faults — we handle both.
Related pages
Official sources
Last updated 2 October 2026. General information only. Every property is different, so call us to talk about yours.