Toilets
How to fix a running toilet
A running toilet is almost always caused by a worn flush valve (flapper or drop valve) letting water leak from the cistern into the bowl, or an inlet valve that will not shut off. Check the flush valve seal first, then the inlet valve and float. Replacing the faulty valve stops the running.
That constant trickle or hiss from the toilet is not just annoying, it is money running down the drain. A running toilet can quietly waste thousands of litres a week, which shows up on your Sydney Water bill. The mechanism inside a cistern is simple though, and once you know the two parts that usually fail, diagnosing it is straightforward.
How a toilet cistern works
When you flush, the flush valve at the bottom of the cistern opens and lets the stored water rush into the bowl. It then closes, and the inlet valve opens to refill the cistern. A float rises with the water level and shuts the inlet valve off once it is full. If either valve fails to seal, water keeps moving and the toilet runs.
Diagnose which valve is at fault
Take the cistern lid off and watch. There are two common scenarios:
- Water is trickling into the bowl and the cistern slowly empties and refills. That is the flush valve, the rubber seal or flapper at the bottom is worn or not seating properly.
- Water keeps flowing in and the level rises up to and over the overflow tube. That is the inlet valve or float, it is not shutting off at the right level.
A simple test: put a few drops of food colouring in the cistern and wait 15 minutes without flushing. If colour appears in the bowl, the flush valve seal is leaking.
Fixing it
For a worn flush valve seal or flapper, turn off the toilet stop tap (usually on the wall behind or below the cistern), flush to empty the water, and inspect the seal. A perished or gritty seal can often be cleaned or replaced with a matching part. For an inlet valve that will not shut off, check the float first, sometimes it just needs adjusting to a lower level so it closes earlier. If the inlet valve itself is worn, it needs replacing.
Many modern Australian toilets use a combined drop valve, and getting the right replacement part matters, as there are dozens of variations. This is where a lot of DIY jobs stall.
Terry has repaired and replaced toilet cisterns across Berala, Regents Park and the inner west since 1986, and he carries common valves and seals on the van, so a running toilet is often a same-visit fix.
When to call a plumber
Call a plumber if you cannot identify the faulty part, if the stop tap is seized or leaking, if the cistern is cracked, or if replacing the valve has not stopped the running. A running toilet that has soaked into the floor or is leaking at the base is also a job for a licensed plumber. Terry will give you a fixed quote before any work. Call him on 0415 274 542.
Frequently asked questions
- How much water does a running toilet waste?
- A running toilet can waste anywhere from a few hundred to several thousand litres a day depending on the leak. Even a slow trickle adds up quickly on your water bill, so it is worth fixing promptly.
- How do I know if it is the flush valve or the inlet valve?
- If water trickles into the bowl and the cistern slowly drains, it is the flush valve seal. If water keeps flowing in and rises to the overflow tube, it is the inlet valve or float not shutting off. The food-colouring test in the cistern confirms a leaking flush valve.
- Can I fix a running toilet myself?
- Often yes, if it is a worn seal or a float that needs adjusting. The main challenge is identifying and sourcing the correct replacement valve, as there are many variations. If you cannot find the part or the stop tap is seized, call a plumber.
- Where is the toilet stop tap?
- The stop tap is usually on the wall or floor directly behind or below the cistern, a small tap on the water supply line. Turn it clockwise to shut off the water before working on the cistern.
- Why does my toilet run intermittently for a few seconds?
- A toilet that briefly runs on its own, sometimes called phantom flushing, is usually a slow leak past the flush valve seal that drops the water level until the inlet valve tops it up. A worn or dirty flush valve seal is the usual cause.
Related services
Need a hand from a real plumber?
Terry's been sorting plumbing across Berala and Western Sydney since 1986. Call 0415 274 542 for a straight answer and a fixed price.
NSW Licence L10959 · 40+ years experience