A dripping shower mixer is one of those small annoyances that can quietly cost you a surprising amount on your water bill — and in New Zealand, where water charges are increasingly common, it pays to sort it out promptly. The good news is that many shower mixer drips are caused by worn internal parts that a confident DIYer can replace. Here's how to work out what's going on and what to do about it.
Why Is My Shower Mixer Dripping?
Most shower mixers drip for one of a few common reasons:
- Worn cartridge or ceramic disc — the most common cause in modern single-lever mixers
- Worn O-rings or rubber washers — more common in older two-tap (hot and cold) shower sets
- Damaged valve seat — the surface the washer presses against can corrode or pit over time
- Faulty thermostatic cartridge — found in thermostatic mixer showers, these can fail and allow water to seep through
- High water pressure — if your home's pressure is too high, it can cause dripping and accelerate wear on internal parts
Before you pull anything apart, check whether the drip is coming from the showerhead, the mixer body itself, or from a connection behind the wall. Each points to a different fix.
What You'll Need
For most cartridge or washer replacements, gather:
- Adjustable spanner and/or basin wrench
- Flathead and Phillips screwdrivers
- Allen key (hex key) set
- Replacement cartridge, O-rings, or washers (match your brand and model)
- Plumber's grease (silicone-based)
- A cloth or small bucket to catch residual water
- Masking tape to protect chrome finishes
Replacement cartridges are available from Mitre 10 and Bunnings. Take your old cartridge in-store to match it up, or note the brand and model of your mixer before you go.
Step 1 — Turn Off the Water Supply
Always isolate the water supply before opening any mixer. Look for an isolating valve on the hot and cold pipes feeding the shower — often located in a nearby cupboard or behind an access panel. If there's no isolator, you'll need to turn off the water at the toby (main stopcock), usually near the boundary of your property.
Once isolated, turn the mixer on to release any pressure and drain residual water from the pipes.
Step 2 — Disassemble the Mixer
- Remove the handle. Most single-lever handles have a small cap on top hiding a screw — pop it off with a flathead screwdriver and undo the screw beneath.
- Pull the handle off. It may need a gentle wiggle.
- Unscrew or unclip the trim plate (the decorative cover around the mixer body).
- You should now see the cartridge or valve assembly.
Take photos at each stage so you can reassemble correctly.
Step 3 — Replace the Cartridge or Washers
Cartridge-style mixers
Note the orientation of the cartridge before removing it — most are directional. Unscrew the retaining nut or clip, pull the cartridge straight out, and take it to your hardware store to find a match. Fit the new cartridge in the same orientation, reassemble in reverse order, and apply a small amount of silicone plumber's grease to any O-rings.
Washer-style (older two-tap) mixers
Unscrew the packing nut, remove the spindle, and replace the rubber washer at the bottom. If the valve seat feels rough, a valve seat grinder tool (available from plumbing suppliers) can smooth it out. Replace any O-rings on the spindle at the same time.
Step 4 — Reassemble and Test
Reassemble the mixer, turn the water supply back on slowly, and check for leaks before replacing the trim plate. Run the shower briefly and confirm the drip has stopped.
Checking Your Water Pressure
If your mixer keeps wearing out prematurely, high water pressure could be the culprit. BRANZ and the NZ Building Code (clause G12) specify that household water pressure should generally not exceed 500 kPa at the point of use. A licensed plumber can test your pressure and fit a pressure-limiting valve if needed.
Thermostatic Mixers — A Note of Caution
Thermostatic shower mixers are more complex. They contain a thermostatic element that regulates temperature to prevent scalding — an important safety feature, particularly under the Healthy Homes Standards for rental properties. While cartridge replacement is technically similar, incorrect reassembly can compromise the temperature-limiting function. If in doubt, have a licensed plumber carry out this repair.
When to Call a Professional
Some shower plumbing work in New Zealand is restricted work under the Plumbers, Gasfitters and Drainlayers Act 2006, meaning it must be carried out by a licensed tradesperson registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). This includes:
- Any work on pipes within the wall (e.g., moving or replacing supply lines)
- Installing a new shower mixer or replacing the valve body
- Work on hot water systems
Replacing a cartridge or washer within an existing mixer is generally considered maintenance and can be done by a homeowner — but if you're unsure, it's always safer to call a pro.
You should also call a licensed plumber if:
- The drip is coming from inside the wall
- You can't identify or source the correct replacement parts
- The valve seat is badly damaged
- Water pressure issues are suspected
- The mixer is old and may be better replaced entirely
A qualified local plumber can be found quickly on tradedirectory.co.nz.