A constantly running toilet can waste up to 200 litres of water per day — that's roughly $150–$300 extra on your annual water bill. The good news: most running toilets are caused by one of five simple, fixable problems. Most can be repaired in under 30 minutes with parts costing $5–$25 from Bunnings.
How to Tell If Your Toilet Is Running
Before you diagnose the cause, confirm the toilet is actually running. Here are three quick checks:
- Listen carefully for a hissing or trickling sound coming from the cistern between flushes. This is the most common indicator that water is escaping continuously.
- The food colouring test: Put a few drops of food colouring (or a toilet dye tablet) into the cistern. If colour appears in the bowl within 15 minutes without flushing, water is leaking through the flush valve — the flapper is almost certainly to blame.
- Check the overflow tube: Remove the cistern lid and look inside. If water is flowing into the central overflow tube (the tall plastic pipe in the middle of the cistern), the water level is set too high. This will cause the toilet to run continuously as water drains away.
Quick tip: The cistern lid simply lifts off — no tools needed. Inspecting inside the cistern is the fastest way to identify what's going wrong.
The 5 Most Common Causes
The vast majority of running toilets come down to one of these five issues. Work through them in order — the flapper is by far the most common culprit.
1. Worn or Warped Flapper
The flapper is the rubber seal at the bottom of the cistern. It lifts when you flush and drops back down to seal the flush valve so the cistern can refill. Over time — usually every 3–5 years — the rubber warps, cracks, or builds up mineral deposits and no longer seals properly. Water trickles continuously from the cistern into the bowl, even when you haven't flushed.
The fixReplace the flapper. Parts cost $5–$12 at Bunnings and replacement takes about 10 minutes. This is the easiest toilet repair you can do yourself — see the step-by-step guide below.
2. Faulty Fill Valve
The fill valve (also called a ballcock) controls the flow of water into the cistern after a flush. When it wears out, it doesn't shut off cleanly — the cistern overfills, or water trickles constantly even when the cistern is already full. You'll usually hear a persistent hissing sound. In older toilets, the fill valve is a ballcock with a float arm; in modern toilets, it's a vertical fill valve with a cup float.
The fixReplace the fill valve. Parts cost $15–$30 and the job is moderate DIY — you'll need to turn off the water supply and disconnect the inlet hose. Allow about 30 minutes.
3. Float Set Too High
The float — either a ball float on an arm, or a cup float that slides up a vertical shaft — tells the fill valve when to stop letting water in. If the float is set too high, the water level rises above the top of the overflow tube and drains away constantly. The fill valve never shuts off because the target water level is never reached.
The fixAdjust the float arm downward (on ball float systems) or slide the cup float down its shaft (on modern systems) to lower the target water level. No parts needed — see the adjustment guide below.
4. Damaged Flush Valve Seat
The valve seat is the smooth rim that the flapper presses against to create a watertight seal. If the seat is cracked, corroded, or scaled with mineral deposits, even a brand-new flapper won't seal correctly. Water will seep through regardless of how many flappers you replace.
The fixFor light mineral scale, clean the seat with fine steel wool or a descaling solution. If the seat is cracked or deeply corroded, the flush valve will need replacing ($20–$40, moderate DIY). If you've already replaced the flapper and the toilet is still running, inspect the seat carefully.
5. Overflow Tube Too Short
The overflow tube is a fail-safe — if the water level gets too high, it drains into the bowl rather than overflowing the cistern. If the tube has been cut too short for the cistern's water level setting, water will drain down it constantly even when the float is set correctly.
The fixLower the water level so it sits 2–3cm below the top of the overflow tube. If this isn't possible without affecting flush performance, the overflow tube may need replacing as part of a cistern rebuild kit.
Step-by-Step: Replace a Toilet Flapper
Replacing the flapper is the single most effective toilet repair you can attempt yourself. It fixes the majority of running toilet problems and costs almost nothing. Here's how to do it:
Turn off the water supply
Find the isolation valve on the water supply pipe behind or beside the toilet base. Turn it clockwise until it stops. If there's no isolation valve, turn off the main water supply at the meter.
Flush to empty the cistern
Flush the toilet once to drain as much water as possible from the cistern. Remove the cistern lid and set it aside on a towel — cistern lids are heavy and can crack if dropped.
Remove the old flapper
Unhook the flapper from the two pegs (ears) on either side of the flush valve. The flapper simply pulls off — no tools required. Note how it sits so you can match the orientation of the new one.
Disconnect the chain
Unhook the flapper chain from the flush handle arm. Take note of which hole in the arm it was attached to — this affects how the flapper opens when you flush.
Match and purchase a replacement
Take the old flapper to Bunnings to match the size, or simply buy a universal flapper kit. Most Australian toilets use either a 2-inch or 3-inch flapper. Check the brand name on your cistern — many Bunnings staff can identify the right part from the toilet model.
Install the new flapper
Hook the new flapper onto the pegs on either side of the flush valve. Attach the chain to the flush handle arm, leaving 1–2cm of slack. Too much slack and the flapper won't lift fully; too little and it won't seal properly.
Test the repair
Turn the water supply back on and let the cistern fill completely. Flush once and watch the flapper drop and seal. Check for the hissing sound. Repeat the food colouring test after 15 minutes to confirm the seal is watertight.
Flapper sizing tip: Most Australian toilets use either a 2-inch or 3-inch flapper. If in doubt, buy a universal kit — they include multiple sizes and adapt to most cistern configurations. Caroma, Fowler, and Raymor are the most common Australian brands.
Step-by-Step: Adjust the Float
If the water level in your cistern is sitting at or above the top of the overflow tube, you need to lower the float. The method depends on what type of float your toilet has:
Ball float (older toilets)
The ball float is a plastic or copper sphere on the end of a horizontal arm. To lower the water level, gently bend the float arm slightly downward — this causes the float to trigger shutoff at a lower water level. Some older toilets have an adjustment screw at the pivot point of the arm; turn it anti-clockwise to lower the shutoff level.
Cup float (modern toilets)
The cup float is a cylindrical float that slides up and down a vertical fill valve shaft. To lower the water level, pinch the adjustment clip on the side of the float and slide the float down the shaft. Release the clip to lock it in the new position. The further down the shaft you set the float, the lower the water level will be.
In both cases, the water level should sit approximately 2–3cm below the top of the overflow tube when the cistern is full. Adjust, let the cistern refill, then check the level against the overflow tube. Repeat as needed until the water stops draining into the tube.
The correct water level is often marked on the inside wall of the cistern with a moulded line or text reading "water line". Use this as your guide if it's visible.
How Much Does a Plumber Charge to Fix a Running Toilet?
Most running toilet repairs are affordable DIY jobs. Here's a comparison of what you'd spend doing it yourself versus calling a licensed plumber:
| Fix | DIY cost | Plumber cost |
|---|---|---|
| Flapper replacement | $5–$15 | $120–$200 |
| Fill valve replacement | $15–$30 | $150–$220 |
| Float adjustment | $0 | $100–$150 |
| Full cistern rebuild kit | $30–$60 | $180–$280 |
| New toilet suite (if needed) | $150–$600 | $350–$900 installed |
Plumber labour rates vary significantly across Australia — Sydney and Melbourne tend to be at the higher end. Most plumbers charge a call-out fee of $80–$150 on top of the labour and parts. If the repair is simple (flapper only), the call-out fee will make up the majority of the cost.
Replacing a flapper or adjusting a float is legal DIY in all Australian states — no licence required. However, if the toilet needs new water supply connections or the pan is cracked, you'll need a licensed plumber.
When to Call a Plumber
Most running toilet repairs are well within DIY range. But there are times when it makes sense to call a licensed plumber:
- The toilet is still running after you've replaced the flapper and adjusted the float. This suggests a damaged flush valve seat or a failing fill valve — both can be DIY, but if you're not confident, a plumber can diagnose and fix it in one visit.
- Water is on the floor around the toilet base. This is a different problem entirely — it could indicate a cracked pan, a failed wax seal (also called a P-trap seal), or a loose connection. Turn off the isolation valve immediately and call a plumber.
- Multiple parts are failing at once. If the flapper, fill valve, and float are all worn out, your cistern suite may be near the end of its life. A plumber can advise whether a full suite replacement is more economical than ongoing repairs.
- Your water bill has spiked unexpectedly. If you're on a meter and the bill is much higher than normal, a plumber can check for hidden leaks throughout the property — not just the toilet.
Never ignore water on the floor. If water is pooling around the base of the toilet or leaking from the cistern, turn off the isolation valve immediately and call a licensed plumber. Left untreated, water damage to flooring and subfloor can cost thousands to repair.
Frequently Asked Questions
The most common cause is a worn flapper that isn't sealing the flush valve properly. Water continuously trickles from the cistern into the bowl. Try pressing down on the flapper with your finger — if the running stops, the flapper needs replacing. This is a simple $5–$15 DIY fix available at any Bunnings.
A continuously running toilet wastes between 60 and 200 litres of water per day depending on the severity of the leak. Over a year, that's 20,000–70,000 litres — adding $100–$300 or more to your water bill. If you're on a meter, a running toilet can be one of the most expensive plumbing problems in the home.
No. A running toilet won't resolve on its own and will typically get worse over time as parts continue to wear. It's worth fixing promptly both to save water and avoid a larger repair bill later. Rubber flappers in particular tend to deteriorate faster once they begin to warp.
The cause is the same regardless of time of day — usually a faulty flapper or fill valve. Fixing the underlying issue is the only solution. As a temporary measure, you can turn off the isolation valve behind the toilet before bed, but this means you won't be able to flush overnight. Address the root cause as soon as possible.
Not usually — unless water is leaking onto the floor, in which case turn off the isolation valve immediately and call a plumber. A toilet that runs between flushes is wasteful but not urgent. However, it should be fixed within a week or two to avoid an expensive water bill and prevent further wear on cistern components.
Add a few drops of food dye or a toilet dye tablet to the cistern. Wait 15 minutes without flushing. If colour appears in the bowl, the flapper isn't sealing and needs replacing. You can also press down on the flapper with your finger — if the running sound stops immediately, that confirms the flapper is the problem.