That constant sound.
A faint hiss. Water trickling. The cistern refilling again and again.
A running toilet might seem minor but it quietly wastes thousands of litres of water every year. That shows up on your water bill, and it only gets worse over time.
The good news?
Most issues are simple to fix.
If you’re trying to figure out how to fix a running toilet, it usually comes down to a handful of common problems, many of which you can sort out in under an hour.
How a Toilet Works (Quick Breakdown)
Before fixing anything, it helps to understand the basics:
- You press the flush button
- The flush valve opens and water flows into the bowl
- The cistern empties and the valve closes
- The fill valve refills the tank
- A float rises with the water
- Once it reaches the set level, the fill valve shuts off
If any part of that process fails, the toilet keeps running.
1. Worn Flush Valve Seal (Most Common Cause)
At the bottom of the cistern is a rubber or silicone seal. Its job is to hold water in the tank.
Over time, it wears out or gets mineral build up allowing water to slowly leak into the bowl.
Signs:
- Constant trickling into the bowl
- The cistern keeps refilling
Fix:
- Turn off water at the isolation tap
- Flush to empty the cistern
- Remove the old seal
- Replace with a matching new one
- Reassemble and turn water back on
This is a cheap part and a quick fix. It is often the solution before needing any toilet repairs.
2. Float Set Too High
The float controls when the fill valve shuts off.
If it’s set too high, water rises above the overflow tube and keeps draining into the bowl.
Fix:
- Remove the lid
- Flush and watch the refill level
- If water reaches the overflow tube, lower the float
- Adjust via screw or clip on the fill valve
Aim for water level about 2cm below the overflow tube.
3. Faulty Fill Valve
The fill valve controls water entering the cistern.
If it’s worn or blocked, it may not shut off properly.
Signs:
- Water keeps running even when full
- Hissing or whistling sound
- Moving the float temporarily stops it
Fix:
- Try cleaning it first by removing the cap and rinsing debris
- If that fails, replace the valve
Most modern valves are universal and easy to swap, but if unsure, a professional plumbing service can handle it quickly.
4. Stuck Flush Button or Chain
Sometimes it’s not a plumbing issue. It’s mechanical.
A stuck button or tangled chain can hold the valve slightly open.
Fix:
- Press the button a few times and check if it returns properly
- Clean around the button housing
For chain systems:
- Ensure it’s not tangled
- Adjust length so it has slight slack
5. Cracked Overflow Tube (Less Common)
If the overflow tube is cracked below the waterline, water drains continuously into the bowl.
Fix:
Usually requires replacing the flush valve assembly.
This is best handled by a licensed plumber if you are not confident.
When to Call a Plumber
DIY fixes work most of the time but not always.
Call a plumber if:
- The problem keeps coming back
- Parts are old, corroded, or hard to replace
- Water is leaking onto the floor
- The toilet or cistern is cracked
- You have a concealed in wall cistern
A plumber can usually fix it in under an hour with the right parts on hand. You can book a plumbing service to get it sorted quickly.
Why You Shouldn’t Ignore It
A running toilet isn’t urgent but it is expensive.
- Up to 25,000 litres of water wasted per year
- Higher water bills
- Ongoing wear on internal components
A small issue can turn into a bigger plumbing problem over time, leading to more extensive plumbing repairs.
Final Thoughts
Most running toilets are caused by simple wear and tear and nothing major.
A small seal replacement, a quick adjustment, or a valve clean is often all it takes to stop the problem.
Ignore it, and you are literally pouring money down the drain.
Fix it early, and it is a quick and cost effective job done.