A toilet that runs for a few seconds and then stops — sometimes called phantom flushing or ghost flushing — is almost always caused by water slowly leaking from the cistern into the bowl. When the water level drops enough, the fill valve kicks in briefly to top it up, then shuts off again. The good news is that in most cases this is a straightforward DIY repair that doesn't require a licensed plumber.
Why This Matters
Beyond the annoying sound, a running toilet can waste a surprising amount of water. Even short, repeated refill cycles add up over a day. Fixing it promptly is good for your water bill and for NZ's water resources — especially if you're on a metered supply.
How Your Cistern Works
Before diving into fixes, it helps to understand the two main components inside your cistern:
- Flapper (or flush valve seal): A rubber seal that sits at the bottom of the cistern and holds water in until you flush. Over time it warps, hardens, or gets coated with mineral deposits and no longer seals properly.
- Fill valve (ballcock): Controls the refill of water after a flush. It's connected to a float — either a ball float on an arm or a cup float that rides up and down the fill valve shaft — which tells the valve when to stop filling.
Step 1 — Diagnose the Problem
Start with a simple dye test:
- Remove the cistern lid and place a few drops of food colouring (or a dye tablet) into the cistern water.
- Wait 10–15 minutes without flushing.
- Check the toilet bowl. If colour appears in the bowl, water is leaking past the flapper.
If no colour appears but the toilet still runs occasionally, the float may be set too high, causing water to trickle into the overflow tube.
Step 2 — Check the Overflow Tube
Look inside the cistern while it's full. Is water trickling down the overflow tube (the tall plastic tube in the centre of the cistern)? If so, your float is set too high and the cistern is overfilling.
- Ball float arm: Gently bend the arm downward slightly so the float sits lower and shuts off the fill valve sooner.
- Cup float: Pinch the clip or turn the adjustment screw on the fill valve shaft to lower the float. The water level should sit about 25 mm below the top of the overflow tube.
Step 3 — Replace the Flapper
If the dye test confirmed a leak, replacing the flapper is usually the fix. This is a common DIY job:
- Turn off the isolating valve (the small valve on the water supply pipe behind or below the toilet). If there isn't one, turn off the water at the toby (main stopcock).
- Flush to empty the cistern.
- 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 Bunnings or Mitre 10 to match the size and style — flappers are not universal.
- Fit the new flapper, reconnect the chain (leave about 1–2 cm of slack), turn the water back on, and test.
Tip: If the flush valve seat (the ring the flapper sits on) feels rough or pitted, no flapper will seal properly. You may need to replace the entire flush valve assembly, or call a plumber.
Step 4 — Replace or Adjust the Fill Valve
If the fill valve itself is worn — you might hear a hissing sound or notice it doesn't shut off cleanly — replacement is the next step. Fill valve kits are available at most hardware stores and are designed for DIY installation. Follow the manufacturer's instructions carefully.
- Shut off the water supply and flush the cistern.
- Use a towel and small bucket to mop up remaining water.
- Disconnect the supply hose from the base of the cistern.
- Unscrew the locknut holding the fill valve in place and lift it out.
- Install the new valve, set the float height, reconnect the supply hose, and turn the water back on.
Common Causes at a Glance
| Symptom | Likely Cause | DIY Fix |
|---|---|---|
| Dye appears in bowl | Worn or warped flapper | Replace flapper |
| Water trickling into overflow tube | Float set too high | Adjust float height |
| Hissing fill valve that won't shut off | Faulty fill valve | Replace fill valve |
| Intermittent running, no obvious cause | Combination of above | Check all three |
NZ-Specific Considerations
NZ water supplies vary in hardness and mineral content depending on your region. Hard water (common in parts of Canterbury and Hawke's Bay) can accelerate wear on rubber flappers and valve seats. If you find yourself replacing flappers frequently, consider a higher-quality silicone flapper.
All plumbing work in New Zealand must comply with the NZ Building Code — specifically Clause G12 (Water Supplies). Replacing internal cistern components like flappers and fill valves is generally considered maintenance and does not require a building consent. However, if you're unsure, check with your local council. You can find more guidance at MBIE Building Performance.
When to Call a Professional
While cistern repairs are generally DIY-friendly, call a licensed plumber if:
- The flush valve seat is cracked or corroded and needs replacing.
- You need to replace the entire cistern or pan.
- There's a leak at the base of the toilet or at supply connections (this involves restricted plumbing work under the Plumbers, Gasfitters and Drainlayers Board rules — only a registered tradesperson may carry out sanitary plumbing work beyond basic maintenance).
- You're not confident working with the water supply.
A qualified local plumber can diagnose and fix the problem quickly. You can find licensed plumbers in your area at tradedirectory.co.nz.
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