Quick Answer
A constantly running toilet is almost always caused by a faulty flapper valve, float set too high, or a worn fill valve — all fixable yourself for $10–$50 in parts. Left unrepaired, a running toilet wastes 200–400 litres of water per day, adding $200–$600 per year to your water bill in Victoria.
If your toilet keeps running long after flushing — or runs in short bursts every few minutes — you’re losing water and money around the clock. Most running toilet problems come down to three parts inside the cistern, all cheap and easy to replace without a licensed plumber.
The Three Main Causes of a Running Toilet
1. Faulty Flapper Valve
The flapper is a rubber seal at the bottom of the cistern that lifts when you flush and drops back to let the cistern refill. When the rubber perishes — common in Melbourne homes with chlorinated water — it no longer seals properly. Water slowly drains from cistern to bowl, and the fill valve runs continuously to keep up.
How to tell: Put a few drops of food colouring in the cistern. Wait 15 minutes without flushing. If colour appears in the bowl, the flapper is leaking.
2. Float Set Too High
The float controls when the fill valve shuts off. If the float arm is set too high, water rises above the overflow tube and drains down it constantly — you’ll hear a steady trickle into the bowl. This is extremely common in older homes with ball-float mechanisms.
How to tell: Look into the cistern. If water is draining into the tall open pipe in the centre (the overflow tube), the float is set too high.
3. Worn Fill Valve (Ballcock)
The fill valve refills the cistern after each flush. When the diaphragm or seals inside wear out, it can’t fully shut off and water dribbles through continuously. You’ll hear a faint hissing sound even when nothing should be running.
How to Fix a Running Toilet: Step-by-Step
What You’ll Need
| Item | Cost | Where to Buy |
|---|---|---|
| Replacement flapper valve (Caroma, Fowler, or universal) | $8–$22 | Bunnings, Reece Plumbing, Mitre 10 |
| Replacement fill valve (Caroma, Dorf, Holby) | $18–$55 | Bunnings, Reece Plumbing |
| Adjustable spanner (medium) | $15–$40 | Total Tools, Bunnings |
| Bucket and old towel | $0 | Already at home |
| Rubber gloves | $5–$12 | Hardware or supermarket |
Step 1: Turn Off the Water Supply and Empty the Cistern
Turn the isolation valve clockwise until closed — it’s on the supply pipe coming from the wall or floor behind the toilet. Flush to empty the cistern. If there’s no isolation valve, turn off the water at the mains stopcock (usually in the front garden or meter box).
Step 2: Identify the Problem
With the lid off, do the food-colouring test for the flapper and check whether water is draining down the overflow tube. This tells you which part needs replacing before you spend money on parts.
Step 3: Replace the Flapper Valve
Unhook the flapper’s ears from the pegs on either side of the flush valve seat. Disconnect the lift chain from the flush handle arm. Take the old flapper to Bunnings or Reece and match it by brand if possible — Caroma and Fowler both use brand-specific flappers that seal better than generic versions on Australian cisterns. Hook on the new flapper, reconnect the chain (leave 1–2 cm of slack), and restore water.
Step 4: Adjust or Replace the Float
On a ball-float arm, bend the arm gently downward so the float sits lower — this drops the water cutoff level below the overflow tube. On a modern tower-style fill valve, there’s usually a clip or dial on the side that adjusts the fill height. Set the water level 25mm below the top of the overflow tube.
Step 5: Replace the Fill Valve If Needed
Disconnect the water supply hose from the bottom of the cistern (have a towel ready). Unscrew the locknut underneath and lift out the old fill valve. Insert the new valve, tighten the locknut hand-tight plus a quarter turn with a spanner, reconnect the supply hose, and restore water. Adjust the float to set the correct fill level.
Step 6: Test and Confirm
Turn water back on slowly and watch the cistern fill. The water should stop 25mm below the overflow tube top. Flush several times and confirm it stops running within 30–40 seconds. Redo the food-colouring test to confirm the flapper seals fully.
Troubleshooting
| Problem | Likely Cause | Fix |
|---|---|---|
| Runs constantly, never stops | Flapper not sealing or water above overflow tube | Replace flapper; adjust float level |
| Short bursts every 10–20 minutes (phantom flush) | Slow flapper leak draining cistern | Food-colouring test to confirm; replace flapper |
| Hissing sound from cistern | Worn fill valve diaphragm | Replace fill valve |
| Water on floor around base | Different problem — wax seal or cracked pan | Call a licensed plumber immediately |
| New flapper still leaks | Wrong brand or damaged valve seat | Try brand-matched flapper; inspect seat for cracks |
When to Call a Licensed Plumber
Most running toilet repairs are safe DIY jobs. Call a VBA-licensed plumber if: water is leaking from the base of the toilet; the cistern is cracked or porcelain is damaged; you can’t isolate the water supply; or the toilet rocks on the floor (damaged floor flange).
Top Tips and Gotchas
- Match the flapper brand. Caroma, Fowler, and Dorf flappers seal better on their own cisterns than generic versions. Check the underside of the cistern lid for the brand name.
- Chain slack matters. Too little slack holds the flapper open slightly, causing phantom flushing. Too much slack lets the chain get caught under the flapper.
- Melbourne’s chlorinated water degrades rubber faster. Flappers in Melbourne typically last 5–7 years. Mark the date on the new one.
- Phantom flush = slow leak costing you money daily. Even if barely noticeable, a phantom-flushing toilet adds hundreds of dollars per year to your water bill.
- Check the fill valve washer before buying a whole unit. Many fill valve failures are just a worn diaphragm washer — available separately for a few dollars at Reece Plumbing.
- Syringe out residual water. After flushing, a turkey baster removes the last 50ml sitting in the cistern bottom so your workspace stays dry.
- Consider upgrading to a dual-flush. Victorian Water Efficiency Labelling requires new toilets to be 4-star WELS rated. If your cistern is over 15 years old, a replacement dual-flush suite saves 40–60% on toilet water usage.
- Night-time running = pressure issue. Mains pressure rises at night when neighbourhood demand drops. A toilet that only runs at night has borderline-worn components — fix them before they fail completely.
Local Melbourne Resources
- Bunnings — Toilet Cistern Parts & Flappers
- Reece Plumbing — Caroma, Fowler & Dorf cistern parts
- Victorian Building Authority — Find a Licensed Plumber
- Melbourne Water — Water Conservation Tips
FAQ
How much water does a running toilet waste?
A slow flapper leak wastes around 200 litres per day. A toilet with water running constantly down the overflow tube can waste 400–800 litres per day. At current Melbourne water rates, that’s $200–$600 extra per year on top of normal usage.
Can I fix a running toilet myself or do I need a plumber?
In most cases, yes — flapper, float, and fill valve replacements are all DIY-safe in Victoria and don’t require a plumbing licence. You only need a licensed plumber if the leak is from the base of the toilet, the cistern is cracked, or there’s no accessible water isolation valve.
How do I know if it’s the flapper or the fill valve?
Use the food-colouring test: add a few drops to the cistern. If colour appears in the bowl without flushing, the flapper is leaking. If the cistern holds its water level but you hear hissing, the fill valve is the problem.
Why does my toilet run at night but not during the day?
Mains water pressure is higher at night when neighbourhood demand drops. Higher pressure forces more water past worn seals. Replace the flapper first as it’s the cheapest fix for a borderline-sealing cistern.
What’s the phantom flush and why does it happen?
A phantom flush is when your toilet spontaneously runs for 10–15 seconds without anyone touching it. It’s caused by a slow flapper leak that silently drains the cistern until the fill valve kicks in. Food-colouring test will confirm it — then replace the flapper.
Final Thoughts
A running toilet is annoying, wasteful, and easy to fix. In most Melbourne homes, replacing a $12 flapper valve takes less than 20 minutes and solves the problem for years. If the flapper doesn’t do it, a new fill valve brings it home for under $50 total in parts — no plumber required, no call-out fee, and no more water bill shock at the end of quarter.