How to Fix a Dripping Single Lever Kitchen Mixer Tap

A dripping single lever kitchen mixer tap is one of the most common household plumbing annoyances — and the good news is that in most cases it's a straightforward DIY fix. The culprit is almost always a worn or damaged ceramic disc cartridge, which controls the flow and temperature of water inside the tap body. Replacing it typically takes under an hour and requires only basic tools.

How a Single Lever Mixer Tap Works

Unlike older taps with rubber washers, single lever mixers use a ceramic disc cartridge — a sealed unit containing two precision-ground ceramic discs that slide against each other to control water flow and temperature. Over time, grit, mineral deposits (common in many NZ regions with hard water), or simple wear can cause these discs to leak, resulting in that annoying drip from the spout or around the base of the lever.

Tools and Materials You'll Need

• Adjustable spanner or basin wrench
• Flathead and Phillips screwdrivers
• Allen key set (hex keys)
• Replacement ceramic cartridge (matching your tap brand/model)
• Plumber's grease (silicone-based)
• Cloth or small bucket
• Torch

Tip: Before buying a cartridge, take a photo of your tap and, if possible, remove the old cartridge to take it to your local plumbing supplier (such as Placemakers or Mitre 10) to match it up. Cartridge sizes and designs vary significantly between brands.

Step 1 — Turn Off the Water Supply

This is the most important first step. Locate the isolating valves under the kitchen sink — there should be one for hot and one for cold. Turn them clockwise until they stop. If your sink doesn't have isolating valves, you'll need to turn off the water at the toby (main stopcock), usually located near the boundary of your property.

Once the supply is off, open the tap lever to release any residual pressure and drain the lines.

Step 2 — Remove the Tap Handle

1. Look for a decorative cap on top of the lever handle — prise it off gently with a flathead screwdriver.
2. Underneath you'll find a screw (Phillips or Allen head). Remove it.
3. Lift or wiggle the handle off the cartridge stem. Some handles are snug — a gentle rocking motion helps.

Step 3 — Access and Remove the Cartridge

1. Once the handle is off, you'll see a retaining nut or collar holding the cartridge in place. Use an adjustable spanner to unscrew it (usually anti-clockwise).
2. Pull the old cartridge straight up and out. Note its orientation — most cartridges have a locating tab or flat side that must align correctly on reassembly.
3. Inspect the cartridge for cracked ceramics, grit, or visible wear.

Step 4 — Install the New Cartridge

1. Apply a small amount of silicone plumber's grease to the O-rings and seating area of the new cartridge.
2. Insert the new cartridge in the same orientation as the old one, ensuring any locating tabs are properly seated.
3. Refit the retaining nut and tighten firmly — but don't overtighten, as this can crack the cartridge body.
4. Reassemble the handle, replace the screw, and refit the decorative cap.

Step 5 — Test for Leaks

Slowly reopen the isolating valves under the sink. Turn the tap on and off a few times, then leave it in the closed position and watch for drips. Check around the base of the spout and under the sink for any signs of weeping. If all is dry — job done!

What If It's Still Dripping?

If the tap still drips after a cartridge replacement, consider these possibilities:

• Wrong cartridge fitted — double-check the part matches your tap model
• Cartridge not seated correctly — remove and refit, checking alignment
• Worn tap body seat — less common, but the brass seating surface inside the tap body can corrode or pit over time, requiring professional attention
• Leak from the base of the spout — this usually indicates worn O-rings on the spout itself, which can be replaced separately

Is This Restricted Plumbing Work?

Replacing a tap cartridge on an existing tap is generally considered maintenance and is something a competent homeowner can do themselves in New Zealand. However, it's important to understand the boundaries. Under NZ law, certain plumbing work is restricted and must be carried out by a licensed plumber registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). This includes installing new tapware, modifying pipework, or any work that connects to or alters the sanitary plumbing system.

If you're unsure whether your intended work crosses into restricted territory, check with the PGDB or MBIE Building Performance before proceeding.

Safety note: Always isolate the water supply before starting any tap work. Never work on a live water line.

When to Call a Professional

Call a licensed plumber if:

• You can't locate or operate the isolating valves or toby
• The tap body itself is cracked or corroded
• There is water damage under the sink suggesting a longer-term leak
• You're not confident identifying the correct cartridge or reassembling the tap
• The work involves modifying or extending any pipework

A qualified local plumber can diagnose and fix the problem quickly and ensure the work meets the NZ Building Code. You can find licensed plumbers in your area at tradedirectory.co.nz.

Sources & Further Reading

• Plumbers, Gasfitters and Drainlayers Board — Licensed tradespeople
• MBIE Building Performance — NZ Building Code guidance
• PlaceMakers — Plumbing supplies
• Mitre 10 — Plumbing and hardware
• BRANZ — Building research and best practice
• WorkSafe NZ — Home safety guidance