A constantly running toilet is one of the most common household plumbing issues in New Zealand — and the good news is it's usually caused by a worn or faulty flap valve (also called a flush valve seal or cistern flapper). In most cases, a homeowner can replace this part themselves without needing a licensed plumber, saving both water and money.
What Is a Flap Valve and Why Does It Fail?
The flap valve sits at the bottom of your toilet cistern and seals the opening between the cistern and the pan. When you flush, it lifts to release water, then drops back down to allow the cistern to refill. Over time, the rubber deteriorates, warps, or builds up mineral deposits — especially in areas with hard water — causing it to no longer seal properly. The result is water continuously trickling from the cistern into the pan.
Signs your flap valve needs replacing:
- You can hear a constant hissing or trickling sound from the toilet
- The toilet refills on its own without being flushed (known as "phantom flushing")
- Placing a few drops of food colouring in the cistern shows colour appearing in the pan without flushing
Tools and Parts You'll Need
Before you start, gather the following:
| Item | Where to Find It |
|---|---|
| Replacement flap valve / flush valve seal | Bunnings, Mitre 10, PlaceMakers |
| Adjustable spanner or pliers | Hardware store or your toolbox |
| Old towels or a bucket | At home |
| Rubber gloves | At home or hardware store |
Important: Flap valves are not universal. Take a photo of your existing valve or, if possible, bring the old one to the store to match it. Common NZ toilet brands include Caroma, Fowler, and Kohler — check your cistern lid or the manufacturer's label for the model number.
Step-by-Step: Replacing a Cistern Flap Valve
1. Turn Off the Water Supply
Locate the isolating valve (also called a stop valve) on the water supply pipe running to the base of the cistern — it's usually on the wall or floor behind the toilet. Turn it clockwise to shut off the water. If there's no isolating valve, you may need to turn off the water at the toby (main stopcock), usually located at the boundary of your property.
2. Flush and Empty the Cistern
Flush the toilet to empty as much water as possible from the cistern. Use a sponge or old towels to soak up any remaining water at the bottom.
3. Remove the Cistern Lid
Lift the lid off carefully and set it aside on a soft surface — cistern lids can crack if dropped.
4. Disconnect the Old Flap Valve
The flap valve is typically clipped or hooked onto a post or ring at the base of the cistern. Unhook the chain or linkage connecting it to the flush handle, then unclip or unscrew the valve from its seat. Some older NZ cisterns use a siphon-style flush mechanism rather than a flap valve — if you see a large plastic siphon unit rather than a simple rubber flap, the repair process is slightly different and may be worth leaving to a plumber.
5. Fit the New Flap Valve
Clip or seat the new valve into position, ensuring it sits flat and centred over the flush valve opening. Reconnect the chain or linkage to the flush handle — there should be a small amount of slack (roughly 1–2 cm) so the valve seals properly when not flushing.
6. Turn the Water Back On and Test
Slowly reopen the isolating valve and allow the cistern to refill. Once full, listen carefully for any trickling sounds. Do the food colouring test again to confirm the seal is watertight. Adjust the chain length if needed.
Is This DIY Work Legal in New Zealand?
Under the NZ Building Code and plumbing regulations, replacing a flap valve or internal cistern components is generally considered routine maintenance that a homeowner can carry out themselves — it does not involve making connections to the water supply pipework. However, any work that involves cutting, joining, or modifying water supply or drainage pipes is restricted work that must be carried out by a licensed plumber registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). Always confirm with your local council if you're unsure.
Water Efficiency: Why It Matters
A leaking toilet cistern can waste thousands of litres of water per year. Energywise and many NZ councils actively encourage homeowners to fix running toilets promptly — both for environmental reasons and to reduce water bills. If you're a landlord, note that under the Healthy Homes Standards, rental properties must have functional plumbing and drainage.
When to Call a Professional
Call a licensed plumber if:
- Your cistern uses an older siphon-style flush mechanism and you're not confident replacing it
- The flush valve seat (the plastic or ceramic ring the flap seals against) is cracked or damaged — this may require cistern replacement
- There is visible water damage, mould, or leaks around the base of the cistern or pan
- You need to install a new isolating valve (this is restricted plumbing work)
- The problem persists after replacing the flap valve
You can find qualified, local plumbers on tradedirectory.co.nz to get the job sorted quickly and correctly.