How to Change a Tap Washer in a Mixer Tap Right

A dripping mixer tap is one of those small domestic frustrations that somehow gets louder every single night. The good news? Most mixer taps don't even use a rubber washer — they rely on a ceramic disc cartridge to control temperature and flow, and replacing one is a manageable DIY task if you know what you're doing. You'll need a handful of basic tools, the correct replacement cartridge (a full ceramic disc cartridge replacement is more like $20–$80), and any part must carry WaterMark certification to meet Australian plumbing regulations. That said, some situations genuinely do call for a licensed plumber.

A concise tutorial demonstrating how to change a washer on a mixer tap, covering the removal process, washer replacement steps, and reassembly — directly supporting this article's practical guidance.
Video Credit: HomeServe

What Is a Tap Washer and Why Does It Fail in a Mixer Tap?

One thing you need to know before getting started is that most people asking about how to change a tap washer in a mixer tap really mean their mixer tap has a leaky spout or a handle that's hard to turn. Most mixer taps don't even use a rubber washer. Instead, they use a ceramic disc cartridge, usually 40mm in diameter, to control temperature and water flow simultaneously from the same mechanism. This is different from a pillar tap, which uses a flat rubber washer that is forced hard against a seat to shut off the water.

Although they can fail, ceramic disc cartridges are more robust than a rubber washer. Over time, calcium from hard water coats and eventually wears down the smooth surfaces of the cartridge disc. In very hard water areas, these can wear out in as little as 12 to 18 months. Ceramic cartridges also frequently develop issues with a cracked disc, worn O-rings, or a rubber seal that has deteriorated around the cartridge body.

If your mixer has any of these issues, you may experience a constant drip from the spout even after turning the mixer off completely, a handle that is difficult to turn, or reduced water flow. These are all signs that either your cartridge or O-rings need attention.

Now that you know what the issue is, you need to gather the right tools before you start working on the mixer.

Labour Day graphic with wrenches, screwdrivers, pliers, nails and bolts arranged as border

Tools and Parts You Need Before You Start

Sort out all your gear and have it close at hand before you start. There's nothing worse than scrambling for a spanner with your mixer half pulled apart — save yourself the grief.

You will need:

• Adjustable spanner

• Flathead screwdriver — good for flicking off decorative caps on the handle

• Phillips-head screwdriver — needed for the handle screw

• Needle-nose pliers — great for grabbing those fiddly little retaining clips

• Shifting spanner — you'll want this to crack the cartridge retaining nut loose

• Silicone grease — dab it on the O-rings before reassembly

• A cloth or small towel — handy for soaking up leftover water inside the tap body

Your mixer's brand and model number — write those down before you head to the shop. Diameter matters a lot — 40mm is the standard size in Australian mixer taps — but don't overlook fixing-tab count and spindle height, which vary between cartridges as well. If you can, get a photo of both the tap and the old cartridge, then take those images along to a plumbing supplies specialist. Expect to pay roughly $5–$30 for a rubber washer and O-ring kit; a full ceramic disc cartridge replacement is more like $20–$80. Any replacement part needs WaterMark certification — Australian plumbing regulations can see non-certified components knocked back on inspection.

Tools ready, replacement part confirmed — cut the water supply first and you're away.

Exploded diagram of mixer tap parts and isolation valve with labelled components

Cut the Water and Expose the Cartridge or Washer

Peek under the basin — that's where the isolation valve lives. Each supply line — hot and cold — should have its own small inline valve, and most take a flathead screwdriver. Turn both valves clockwise as far as they'll go. Can't find isolation valves? Lots of older homes were never fitted with them — the mains stopcock is your fallback. Crack the tap handle wide open — that'll bleed off whatever pressure is still sitting in the line.

There's a small decorative cap on top of the handle — pry or thread it off and you're in reach of the cartridge. A cloth wrapped around your flathead screwdriver lets you ease the cap off without scratching the finish. Lift the cap and you'll find either a Phillips-head screw or a grub screw — the latter needs a hex key. Back the screw out, then give the handle a firm straight pull to free it. Handle gone — the cartridge retaining nut is sitting right there waiting for you. Supply cut, handle removed — you've got clear access to the cartridge or washer.

Hands comparing old worn brass tap cartridge with new replacement in plastic packaging

How to Change a Tap Washer in a Mixer Tap

Here is a step-by-step guide to removing and replacing the component. Using an adjustable spanner, turn the cartridge retaining nut anti-clockwise to undo it. Retaining nuts are typically 22–27mm across flats, so confirm you have the right spanner size first. Once the nut is off, grip the cartridge with pliers and pull it straight up and out. Photograph the cartridge before removing it so you can confirm the correct orientation — installing it upside down will reverse the hot and cold.

Inspect the tap seat where the cartridge sits and seals. If it is pitted or scored, the new cartridge will not seal correctly and the tap will leak again. A pitted seat requires a licensed plumber to re-seat it. If the seat is sound, apply a small amount of silicone grease to the O-rings on the new cartridge. Push the cartridge in with the correct orientation, thread on the retaining nut by hand, then snug it a quarter turn with the spanner — do not over-tighten or the cartridge body may crack.

While you have the tap apart, it is also a good opportunity to inspect the seals and fixings on any over bath shower screens nearby.

DIY tap handle screw tightening versus cracked tap body requiring licensed plumber

Testing, Reassembly, and When to Call a Licensed Plumber

Refit the handle, tighten the handle screw or grub screw, and replace the decorative cap. Turn the isolation valves on slowly and watch the retaining nut area for drips. If you see a drip, tighten a further quarter turn. A few seconds of air and trickle from the spout as the water comes back on is normal.

If the tap continues to leak after a minute or so, the cartridge may not be seated correctly. Turn the isolation valve off and call a licensed plumber. Do not keep tightening the retaining nut — you risk splitting the tap body.

Hot water temperature: Australian plumbing standards require that hot water at bathroom outlets does not exceed 50°C. Do not adjust the tempering valve — that is licensed plumbing work.

The DIY boundary: Rules differ across states and territories, so check your state/territory requirements before you start. In many states, replacing a tap washer or cartridge is permitted as a DIY task. However, installing or replacing tapware directly connected to a water supply pipe is licensed plumbing work in every state and territory.

If you find yourself frequently replacing washers and cartridges, consider whether a new tap is the better investment. Freestanding bath tapware from quality brands like Fienza, Meir, and Bella Vista is built to last, with short basin mixer replacement units starting from $56. Premium tap brands carry warranties of 10 or 15 years, so a new tap often pays off over time. If your plumber is already on site, it is worth replacing the bath hose at the same time — it is a low-cost addition that makes sense to do while the work is underway.

Learning how to change a tap washer in a mixer tap is genuinely useful. But knowing when to call a licensed plumber is just as important.

References

AS 3718:2021 Water supply — Tap ware (incorporating Amendment No. 1:2024), Standards Australia

WaterMark Certification Scheme, Australian Building Codes Board

AS/NZS 3500.4:2025 Plumbing and Drainage — Heated Water Services, Standards Australia

State and territory plumbing licensing authorities (Building and Plumbing Commission Victoria; Building Commission NSW / NSW Fair Trading; Queensland Building and Construction Commission; Plumbers Licensing Board Western Australia (administered by Building and Energy); Consumer, Building and Occupational Services Tasmania; Access Canberra ACT; Office of the Technical Regulator / Consumer and Business Services South Australia; Plumbers and Drainers Licensing Board Northern Territory)

FAQs

How do I know if my mixer tap uses a ceramic disc cartridge or a rubber O-ring seal?

Ceramic disc cartridges became the norm in mixer taps from the mid-1990s onward — the handle feels smooth and travels through about a 90-degree arc. If the handle swings a full 180 degrees or more and feels springy when you push it down, you're likely dealing with a rubber jumper valve and seat — a design that still shows up in older Australian homes and budget imported fittings.

Will hard water wreck a brand-new ceramic disc cartridge quickly, and is there anything I can do about it?

Absolutely — high-mineral water can have a replacement cartridge showing wear in as little as 12 to 18 months without any protective measures. An inline water filter or softener on the supply lines is your best defence, and a wipe-down of the disc surfaces with white vinegar at each future service keeps early mineral build-up from turning into a seal failure.

Could I void my tap's warranty if I swap the cartridge out myself?

Plenty of Australian tap warranties are only valid if a licensed plumber does the work, so check the manufacturer's documentation before you touch anything — especially on premium brands, where cover can stretch to 10 or 15 years.