A constantly running or slow-filling toilet is one of the most common household plumbing annoyances — and in many cases, the culprit is a worn-out cistern inlet valve (also called a fill valve or ballcock). The good news is that replacing one is a straightforward DIY job for most homeowners, provided you understand where the legal boundaries lie and take a few basic precautions.
Understanding the Inlet Valve and NZ Regulations
The inlet valve controls the flow of water into your cistern after each flush. Over time, the rubber seals and float mechanism wear out, causing the cistern to overfill, run continuously, or fill very slowly.
In New Zealand, replacing a cistern inlet valve sits in a bit of a grey area. Connecting or disconnecting water supply pipes is restricted plumbing work under the Plumbers, Gasfitters and Drainlayers Act 2006, and must be carried out by a licensed tradesperson registered with the Plumbers Gasfitters & Drainlayers Board. However, replacing internal cistern components — such as the inlet valve, flush valve, or flapper — where you are not disturbing the supply pipework is generally considered maintenance work a homeowner can undertake. If you are unsure, check with your local council or contact a licensed plumber.
Tools and Materials You'll Need
- Adjustable spanner or basin wrench
- Flat-head and Phillips screwdrivers
- Sponge and small bucket
- Old towels
- Replacement inlet valve (universal or brand-matched)
- PTFE tape (plumber's tape)
Replacement inlet valves are widely available at Mitre 10 and Bunnings. Most modern toilets use a bottom-entry float valve (a vertical plastic unit), while older toilets may have a side-entry brass ballcock. Take a photo of your existing valve or bring it to the store to match the fitting.
Step-by-Step: Replacing the Inlet Valve
1. Turn Off the Water Supply
Locate the isolating valve on the supply pipe running to the base of the cistern — it's usually a small inline tap or a slotted screw you turn 90 degrees with a screwdriver. If there is no isolating valve, you'll need to turn off the water at the toby (main stopcock) outside. This is a good time to note that if your toilet lacks an isolating valve, a plumber can fit one easily and it's well worth having.
2. Flush and Empty the Cistern
Flush the toilet to empty the cistern, then use a sponge and bucket to remove any remaining water. Place old towels on the floor to catch drips.
3. Disconnect the Water Supply Hose
Using an adjustable spanner, carefully unscrew the supply hose from the base of the inlet valve (the fitting that comes through the bottom or side of the cistern). Have your bucket ready — some water will drain out. Do not overtighten or force fittings; cistern porcelain can crack.
4. Remove the Old Inlet Valve
Inside the cistern, hold the valve body steady while you unscrew the locknut on the outside of the cistern with your spanner. Once the locknut is off, the valve lifts straight out from inside the cistern. Note how the overflow tube and float arm are positioned before removing.
5. Fit the New Inlet Valve
Insert the new valve through the hole in the base (or side) of the cistern. Ensure the rubber washer or seal sits flush against the inside of the cistern wall. Hand-tighten the locknut on the outside, then snug it up with a spanner — firm but not over-tightened. Wrap a couple of turns of PTFE tape around the supply hose thread before reconnecting it.
6. Adjust the Float Height
Most modern valves have an adjustable float. Set the water level so it sits approximately 10–15 mm below the top of the overflow tube — this prevents water from running into the pan. Follow the manufacturer's instructions for your specific valve.
7. Turn the Water Back On and Test
Slowly open the isolating valve and let the cistern fill. Check all connections for leaks. Flush a couple of times and watch the fill cycle — the cistern should fill quietly and stop cleanly at the correct level.
Common Problems and Tips
- Cistern still runs after replacement: Check the float height adjustment and ensure the valve is seating fully when the cistern is full.
- Leaking at the locknut: Ensure the rubber washer is correctly seated and the locknut is adequately tightened.
- Noisy filling: Some valves have a flow adjuster — reducing the flow rate can quieten a noisy fill.
- Old brass ballcock: These can sometimes be repaired with a washer kit rather than full replacement, but a modern plastic float valve is generally more reliable and water-efficient.
When to Call a Professional
Call a licensed plumber if:
- There is no isolating valve and you need to work on the main supply line
- The supply pipe connections are corroded, damaged, or leaking
- The cistern itself is cracked or the pan-to-cistern seal is failing
- You are not confident working with the plumbing, or the job expands beyond a simple valve swap
- You are a landlord — under the Healthy Homes Standards, rental properties must have functional plumbing, and using a licensed tradesperson protects you legally
A qualified local plumber can be found quickly on tradedirectory.co.nz.
A Note on Water Efficiency
A leaking inlet valve can waste a surprising amount of water. BRANZ research highlights that toilets are one of the largest water users in NZ homes. Fitting a modern dual-flush compatible valve and keeping your cistern in good repair is a simple way to reduce water waste and lower your water bill.