A landlord in Ingleburn asked me to look at a rental where the tenant had mentioned the toilet hisses a bit. The water bill had nearly doubled. The cistern had been running for months, a trickle over the top of the overflow day and night, quiet enough that nobody thought it was a problem. Sydney Water puts a constantly running toilet at thousands of litres a day, and Campbelltown Council's water saving guide uses 96,000 litres a year for a leaking toilet.
When a toilet keeps running, one of two parts has failed: the rubber seal under the outlet valve is letting water trickle into the bowl, or the inlet valve is not shutting off and water is running over the overflow. Both are cheap parts, and the fix took twenty minutes. If you would rather not, we are a toilet and tap plumber, no call-out fee, across South West Sydney.
A toilet keeps running for one of two reasons: the rubber seal under the outlet valve is worn and water trickles into the bowl, or the inlet valve will not shut off and water runs over the overflow tube. Lift the lid: water above the overflow means the inlet valve, water below it but still trickling means the outlet seal. Both are cheap parts, and turning the isolation tap off stops the waste until it is fixed.
How a toilet cistern works
Every dual flush cistern has two valves. The inlet valve (the fill valve) lets water in from the wall, and a float on it shuts the water off at the set water line. The outlet valve, or flush valve, sits in the middle of the cistern over the hole into the bowl. Press the button and it lifts, water drops into the bowl, the float falls, the inlet opens, and the cistern refills until the float rises and closes it again. Inside the outlet valve is a tall overflow tube: if the inlet ever fails to shut, water climbs to the top of that tube and runs into the bowl instead of over the floor. Under the outlet valve is a rubber seal, the flush valve washer, and it is the single most common reason a toilet keeps running.
Two reasons a toilet keeps running
1. The flush valve washer is worn (water trickles into the bowl)
The seal under the outlet valve hardens, warps or picks up grit and stops sealing. Water leaks from the cistern into the bowl in a slow trickle, the level drops, and the inlet valve tops it up. That is the intermittent refill at 2am, the faint shimmer on the back of the bowl, and the hiss that starts and stops for no reason. Hard water makes it worse, and so do the chlorine tablets people drop in the cistern, which eat the rubber.
2. The toilet inlet valve will not shut off (water runs over the overflow)
The inlet valve's diaphragm or seat wears, or grit from the mains jams it open after Sydney Water has worked on the pipes in the street. The float rises, the valve keeps dribbling, and the water level climbs above the overflow tube and runs into the bowl constantly. The sound is a steady hiss that never stops. Sometimes the float has just been knocked down the arm and the water line is set too high.
Then the minor ones: a button stuck down, a broken flush cable holding the outlet valve up, and a cracked cistern, which means replacement.
How to tell which fault you have
Take the lid off and look. If the water is sitting at or above the top of the overflow tube, it is the inlet valve or the float. If the water is below the overflow but you can still see or hear it trickling into the bowl, it is the flush valve washer. For a slow leak you cannot see, Sydney Water's test is a strip of dry toilet paper laid against the back of the bowl above the water line: if it wets without a flush, the cistern is leaking. A few drops of food colouring in the cistern does the same job. For the whole house, the one hour water meter test in the Sydney Water leak detection guide shows whether anything is running.
| Symptom | Likely cause | Fix | DIY? |
|---|---|---|---|
| Hiss that starts and stops, cistern refills on its own | Worn flush valve washer | Replace the outlet valve seal | Usually yes |
| Constant hiss, water above the overflow tube | Inlet valve worn or jammed, float set too high | Adjust the float; replace the inlet valve | Float yes, valve no |
| Cistern not filling, or filling very slowly | Isolation tap part closed, blocked filter, failed valve | Open the tap, clean the filter, replace the valve | Tap and filter yes |
| Button stays down or the flush will not stop | Jammed button, broken cable or linkage | Free or replace the button assembly | Sometimes |
| Water on the floor behind the toilet | Cistern to pan seal, flexi hose, cracked cistern | Reseal or replace | No |
| Toilet cistern leaking into the bowl on an old single flush | Worn parts on a 20 year old unit | Replace the cistern or the suite | No |
What you can fix yourself
Turn the isolation tap behind the toilet off first. If the float is set too high, most inlet valves have a screw or a clip on the float arm: lower it until the water line sits a couple of centimetres below the top of the overflow. If the cistern is not filling, check the isolation tap is fully open, then unscrew the inlet hose at the valve and clean the small mesh filter, which is usually full of grit.
Replacing the flush valve washer on most Caroma and similar dual flush cisterns needs no tools: flush to empty, twist the outlet valve anticlockwise and lift it out, peel the old seal off the bottom, fit the new one, drop it back in and twist to lock. Take the old seal to the plumbing supplier, because there are a dozen shapes. That is the same class of job as changing a tap washer, and it is where sensible DIY ends. Replacing the inlet valve means disconnecting the water supply and the flexi hose, and in NSW work on the water supply is plumbing work for a licensed plumber. If the flexi is more than a few years old I replace it at the same time, because a burst flexi hose does far more damage than a running toilet ever will.
Dual flush cistern repair: what it costs
There is no set price for a toilet cistern repair because the part decides it. A flush valve washer is the cheapest thing in the cistern, an inlet valve costs more, a complete outlet valve more again, and if the cistern is cracked or the suite is a 1990s single flush, replacing it is often better value than feeding it parts. So the job is quoted on inspection, and what moves it is the part and the access (an in-wall cistern behind tiles takes longer than a close coupled one). For labour, Sydney 2026 price guides put plumbers at $92 to $230 an hour, most around $140, with call-out fees of $69 to $170. Most cistern repairs are finished inside the first hour.
A toilet running over the overflow is annoying, but it is never an after-hours emergency. Turn the isolation tap off, turn it back on when you need to flush, and book it for business hours. That saves the emergency rate.
Landlords: a running toilet water bill is yours
If you own a rental in Ingleburn, Campbelltown or anywhere in NSW, this matters twice. You can only pass water usage on to the tenant if the property meets the water efficiency measures, and one of them is no leaking taps or toilets at the start of the tenancy and whenever the measures are checked. Since 23 March 2025 every toilet in the property also has to be dual flush with a WELS rating of three stars or better. An old single flush uses about 11 litres a flush against 4.5 and 3 on a modern dual flush, so the upgrade pays for itself even before you count the leak. I do the inspection, the repairs and the paperwork; details are on the water efficiency certificates page. Done right. Done once.
When to call a plumber
Call when the washer has been replaced and the toilet keeps running anyway, when the cistern will not fill after you have cleaned the filter, when there is water on the floor rather than in the bowl, when the cistern is concealed in the wall, or when the toilet is old enough to replace rather than repair. If the toilet is also slow to flush or blocks, read how to unblock a toilet first, because the cistern is often not the problem. If the meter test says the house is losing water but every toilet checks out, that is a hidden leak: see leaks and burst pipes.
Monarch Civil & Plumbing covers South West Sydney and the Macarthur region from Austral. For a plumber in Ingleburn, a cistern in Cabramatta or anything in between, the toilets, taps and fixtures page covers what I do, and 0455 222 292 gets me directly.
Related guides: toilet cistern replacement.
Need it sorted? Ring 0455 222 292 any hour or book online. Monarch Civil & Plumbing is a toilet and tap plumber, no call-out fee: fixed properly in one visit, quoted before we start.
Need it fixed in Liverpool, Fairfield or Campbelltown?
A toilet that will not clear has its own page: blocked toilet. For taps, cisterns and fixtures see toilets, taps and fixtures, and the suburb pages plumber Liverpool, plumber Fairfield and plumber Campbelltown say what we see locally. No call-out fee, price before we start.
Frequently asked
Why does my toilet keep running after I flush?
Either the rubber seal under the outlet valve (the flush valve washer) has worn and water is trickling from the cistern into the bowl, or the inlet valve is not shutting off and water is running over the top of the overflow tube. Take the cistern lid off: water above the overflow means the inlet valve or float, water below it but still trickling into the bowl means the outlet seal.
How much water does a running toilet waste?
Sydney Water says a constantly running toilet can lose thousands of litres a day, and Campbelltown Council's water saving guide puts a leaking toilet at up to 96,000 litres a year. Even a slow, silent trickle adds up over a quarter. The dry toilet paper test at the back of the bowl, or a few drops of food colouring in the cistern, shows whether yours is leaking.
Can I replace a toilet inlet valve myself?
Adjusting the float and cleaning the inlet filter are fine to do yourself, and so is swapping the outlet valve seal on most dual flush cisterns. Replacing the inlet valve means disconnecting the water supply and the flexi hose, and in NSW that is plumbing work for a licensed plumber. It is a quick job, and the plumber will check the flexi hose and isolation tap at the same time.
Why is my toilet cistern not filling?
Check that the isolation tap behind the toilet is fully open first. Next, unscrew the inlet hose at the valve and clean the small mesh filter, which often clogs with grit after work on the water mains in the street. If the tap is open and the filter is clean, the inlet valve itself has failed or the float is snagged, and the valve needs replacing.
How much does it cost to fix a running toilet?
It depends on the part, so it is quoted on inspection. A flush valve washer is the cheapest fix, an inlet valve costs more, and an in-wall cistern takes longer to access. For labour, Sydney 2026 price guides put plumbers at $92 to $230 an hour, most around $140, with call-out fees of $69 to $170, and most cistern repairs are done inside the first hour in business hours.
Is a running toilet an emergency?
No. Turn the isolation tap behind the toilet off to stop the water, turn it back on when you need to flush, and book a plumber for business hours. The only time to hurry is when water is on the floor rather than in the bowl, because a leaking cistern, flexi hose or pan seal can damage floors and the room below.
Licensed plumber and drainer based in Austral, 13+ years in the trade, working across Liverpool, Fairfield and the Macarthur region. About Paul