How to replace a mixer tap cartridge

Video by Tommy's Trade Secrets. This walk-through is based on the video "Tommy's Trade Secrets - How to Change a Mixer Tap Cartridge" from Tommy's Trade Secrets, a long-running UK DIY and trade tips channel. The video is clear on the key steps and worth watching before you start, particularly the part about identifying the cartridge type before going to buy a replacement.

1. Identify your tap type and the cartridge you need

Not all mixer taps use the same cartridge. The most common type in UK kitchens and bathrooms is a ceramic disc cartridge — a cylindrical unit that controls both hot and cold flow and temperature through a single lever. These come in different sizes and with different spindle configurations, so you cannot just grab any cartridge off the shelf at the builders’ merchant.

The easiest approach is to take the old cartridge out first and bring it with you to match it up in person, or look up your tap brand and model online. Some tap manufacturers sell their own branded cartridges; others use standard sizes that any plumbing supplier will stock. It depends on how old the tap is and where it came from originally.

2. Turn off the water supply and open the tap

Turn off the water supply to the tap. If there are isolation valves on the hot and cold pipes under the sink — small valves with a slot-head screw — turn both of them a quarter turn until the slot is across the pipe. If there are no isolation valves, you will need to turn off at the stopcock, usually found under the kitchen sink or near the front door.

Once the water is off, open the tap fully to release any pressure and drain the residual water from the supply pipes. Put the plug in the sink before you go any further — small screws and cartridge parts have a habit of finding the plughole if you are not careful. A tea towel laid across the basin is a useful extra precaution.

3. Remove the tap handle

Most single-lever mixer taps have a small cap or cover on the front or top of the handle — prise it off gently with a flathead screwdriver. Underneath you will find a retaining screw, usually a Philips or Allen key type. Remove the screw and the handle will slide or lift off.

Some handles are quite stiff, especially on older taps or ones that have not been off before. Do not force it with excessive leverage — try easing it side to side as you pull upwards. A drop of penetrating oil around the base of the handle and left for 20 minutes will usually free a stuck one without any drama.

4. Unscrew and remove the cartridge

With the handle off you will see the cartridge sitting in the tap body, held in place by a retaining nut or collar. Use an adjustable spanner to unscrew the retaining nut — wrap the jaws with tape first if you want to protect the finish on the tap. Turn anticlockwise to loosen.

Once the nut is off, the cartridge should pull straight out. On some taps there is a small grub screw holding the cartridge in place — check before you just yank. If it has been in there a long time and is stuck, a careful wiggle while pulling should free it. Note the orientation as it comes out — some cartridges are directional and need to go back in the same way.

5. Fit the new cartridge

Push the new cartridge into the body in the same orientation as the old one came out. It should seat cleanly into the housing without needing force. If it does not drop in easily, check you have the right one — a cartridge that does not sit flush will leak even after you have reassembled everything.

Refit the retaining nut and tighten it by hand first, then snug it up with the spanner. Do not over-tighten — you are clamping a ceramic component and cracking the new cartridge before you have even turned the water on would be a frustrating way to end the job. Firm is plenty.

6. Refit the handle and test

Slide the handle back onto the spindle and refit the retaining screw. Replace the decorative cap. Before you restore the water supply, double-check the tap is in the closed position so you are not greeted with a face full of water when the isolation valve opens.

Slowly open the isolation valves back up, or turn the stopcock on, and check for leaks around the cartridge retaining nut. A small drip at this point usually means the nut needs another quarter turn. Run the tap through its full range of motion — the handle should move freely, the water should respond immediately, and there should be no drip when it is closed. If it all feels right, job done. That said, keep an eye on it for the first day or two just in case.

When to call a handyman

Call Richard if you cannot identify the cartridge you need, if the tap is an unusual brand or an older model where parts are harder to source, or if you have opened the tap up and found the seat is damaged rather than the cartridge. He also covers situations where there are no isolation valves under the sink and someone needs to be confident working around the main stopcock. Richard handles plumbing repairs across Sandwich and East Kent — get in touch and he can usually sort it quickly.