A constantly running toilet is one of the most common household plumbing problems in New Zealand — and one of the most wasteful. Left unchecked, a leaking cistern can waste thousands of litres of water a month, pushing up your water bill and putting unnecessary strain on the environment. The good news is that many causes are straightforward to diagnose and, in some cases, safe for a homeowner to fix themselves.
How Your Toilet Cistern Works
Before diving into fixes, it helps to understand the basics. When you flush, water rushes from the cistern (the tank at the back or above the bowl) into the pan. Once the cistern empties, a fill valve (also called a ballcock or inlet valve) opens to refill it. A float rises with the water level and signals the fill valve to shut off when the cistern is full. A flapper or flush valve seal sits at the bottom of the cistern and stops water from leaking into the bowl between flushes. If any of these components fail, your toilet can run continuously.
Common Causes of a Running Toilet
1. Worn or Warped Flapper
The flapper is a rubber seal that sits over the flush valve opening. Over time, rubber degrades, warps, or accumulates mineral deposits — especially in areas with harder water. A faulty flapper lets water trickle constantly from the cistern into the bowl. You can confirm this by placing a few drops of food colouring in the cistern; if colour appears in the bowl without flushing, your flapper is leaking.
2. Incorrect Float Height
If the float is set too high, water will rise above the overflow tube and drain continuously into the bowl. You may hear a faint hissing or trickling sound. Adjusting the float arm or the float height on a modern fill valve is usually a simple fix.
3. Faulty Fill Valve
Fill valves wear out over time. A damaged or worn fill valve may not shut off properly, causing the cistern to overfill or run indefinitely. Replacing a fill valve is a moderately straightforward job.
4. Damaged Overflow Tube
If the overflow tube is cracked or set at the wrong height, water can drain away before the cistern reaches the correct level, causing the fill valve to run non-stop.
5. Flush Valve Seat Damage
If the seat that the flapper rests against is pitted or corroded, even a new flapper won't seal properly. In this case, the entire flush valve assembly may need replacing.
Comparing the Most Common Fixes
| Problem | DIY Difficulty | Approximate Parts Cost (guide only) | Likely Fix |
|---|---|---|---|
| Worn flapper | Easy | $5–$20 | Replace flapper |
| Float set too high | Easy | No cost | Adjust float |
| Faulty fill valve | Moderate | $20–$60 | Replace fill valve |
| Damaged overflow tube | Moderate | $15–$40 | Replace tube or assembly |
| Corroded flush valve seat | Harder | $30–$80+ | Replace flush valve |
Parts are available at Bunnings or Mitre 10. Prices are a rough guide only and will vary.
Step-by-Step: Replacing a Flapper
This is the most common fix and well within most homeowners' abilities.
- Turn off the water supply — the isolation valve is usually on the wall or floor behind the toilet. Turn it clockwise to close.
- Flush the toilet to empty the cistern.
- Remove the cistern lid and set it aside carefully — lids can be heavy or fragile.
- Unhook the old flapper from the pegs on the flush valve and disconnect the chain from the flush handle arm.
- Take the old flapper to the hardware store to match the size and style, or check your toilet brand (common NZ brands include Caroma, Fowler, and Roca).
- Snap the new flapper onto the flush valve pegs and attach the chain, leaving a small amount of slack.
- Turn the water back on, let the cistern fill, and test for leaks using the food colouring method.
Adjusting the Float
On older toilets with a ball-float arm, gently bend the arm downward slightly so the float sits lower and the fill valve shuts off before water reaches the overflow tube. On modern fill valves with a cylindrical float, there is usually an adjustment screw or clip on the side of the valve — turn or slide it to lower the water level. The correct water level is typically around 25 mm below the top of the overflow tube.
When to Call a Professional
While replacing a flapper or adjusting a float is considered general maintenance that homeowners can do themselves, some plumbing work in New Zealand is restricted work under the Plumbers, Gasfitters and Drainlayers Board (PGDB) regulations. This includes work on water supply pipes, drainage connections, and certain valve replacements that connect to the mains supply.
If you are unsure whether a repair crosses into restricted work territory, or if:
- The cistern or pan is cracked
- There is water leaking onto the floor
- You've replaced the flapper and fill valve and the problem persists
- The toilet is very old and parts are hard to source
…it's time to call a licensed plumber. A qualified plumber can also check for underlying issues like low water pressure or pipe corrosion. You can find a trusted local plumber on tradedirectory.co.nz.
Safety note: Always turn off the water supply before working inside a cistern, and never attempt to work on mains pressure pipes without the appropriate licence.
Saving Water — It Adds Up
A running toilet is not just annoying — it's costly. BRANZ and Energywise both highlight water efficiency as an important part of a healthy, cost-effective home. If you're a landlord, note that the Healthy Homes Standards require rental properties to be maintained in good working order, which includes plumbing fixtures.