Fix It Britain

A mono mixer, also called a monobloc tap, is a single tap body that sits in one hole in the sink or basin and mixes hot and cold water in one spout. It’s the most common style of tap in modern UK kitchens and bathrooms. Mono mixers go wrong in three main ways: they drip from the spout, they leak under the sink, or they work loose and wobble. Here’s how to fix each one.

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• Difficulty: Easy to moderate. Working in the cupboard under the sink is the awkward part.
• Time needed: 20 minutes to an hour, depending on the fault.
• Useful extra: a torch and a basin wrench or long tap spanner for nuts underneath the sink.

How a mono mixer tap is put together

Knowing the parts makes the repair much easier:

• Cartridges: one large cartridge in a single-lever tap, or two smaller ones (hot and cold) in a two-handle monobloc. These control the flow and are the usual cause of drips.
• Flexible tails: two braided hoses that screw into the underside of the tap and connect to the hot and cold pipes, usually through isolation valves.
• Fixing kit: one or two threaded rods screwed into the base of the tap, with a backplate and nuts underneath the sink that clamp the tap in place.

Fault 1: Mono mixer tap dripping from the spout

A drip from the spout when the tap is off means a cartridge isn’t sealing. Turn off both isolation valves under the sink, open the tap to drain it, then remove the lever or handle (usually held by a grub screw or a screw under a cap). Unscrew the cover and the brass nut, lift out the cartridge and either clean off any limescale or fit an exact replacement. Our mixer tap dripping guide walks through this step by step, including how to match the cartridge and fix a leak at the base of a swivel spout.

Fault 2: Mono mixer leaking under the sink

Clear out the cupboard, dry everything with a towel, then run the tap and watch with a torch. Wrap dry kitchen roll around each joint in turn to find exactly where the water appears.

• Where the flexible tail screws into the tap: these are sealed by a small O-ring and are only meant to be hand-tight plus a little. Turn off the water, unscrew the tail, check the O-ring is seated and undamaged, and screw it back in firmly by hand. If the O-ring is split, replace it or fit a new tail.
• At the isolation valve end of the tail: this is a compression fitting. Hold the valve still with one spanner and nip the nut up a quarter turn with another. Don’t overtighten.
• From the hose itself: if a braided tail is rusty, frayed, kinked or bulging, replace it. Tails are inexpensive, and a burst one can flood a kitchen quickly. Make sure the replacement has the right thread for your tap, which is commonly M10 or M8 on UK monobloc taps.
• From the base of the tap above the sink: water running down the outside of the tap and under the base seal usually comes from the spout O-rings or the cartridge seals, not from the plumbing. Fix the leak at its source rather than adding more sealant.

Fault 3: Loose or wobbly mono mixer tap

A tap that turns or wobbles on the sink has a loose fixing nut underneath. Left alone, the movement can damage the flexible tails and the base seal.

1. Look up under the sink, behind the tap, for the threaded rod and the nut on the backplate.
2. Have a helper hold the tap straight from above.
3. Tighten the nut with a box spanner, basin wrench or long tap spanner until the tap is firm. Don’t crush the base seal or crack a ceramic basin.
4. If the threaded rod spins rather than tightening, it has worked loose from the tap body. Remove the nut and backplate, screw the rod back into the tap by hand, and refit.

Repair or replace your mono mixer?

Repair it if the body is sound and you can get the cartridge. Fantastic Services’ 2026 price guide puts a ceramic cartridge at about £10 to £30. Replace the tap if the chrome is corroded, the body is cracked, parts aren’t available for your brand, or it keeps failing. Any new tap should be suitable for UK water systems; WaterSafe recommends WRAS-approved fittings.

When to call a plumber

Call a plumber if the isolation valves won’t shut off the water, a copper pipe or soldered joint is leaking, a fitting has seized, or water has soaked into the cupboard base or the floor below.

Frequently asked questions

What is a mono mixer tap?

A mono mixer (or monobloc) tap is a single tap body that fits through one hole and mixes hot and cold water in one spout. It can have a single lever or two separate handles.

How tight should monobloc flexible hoses be?

The ends that screw into the tap are sealed by an O-ring, so they only need to be firmly hand-tight. Cranking them up with pliers can split the O-ring or strip the thread in the tap body, which causes leaks.

Why does my mono mixer tap move when I use it?

The fixing nut under the sink has worked loose over time. Tighten it while someone holds the tap straight from above.

Can I replace the flexible hoses on a monobloc tap?

Yes. Turn off the isolation valves, unscrew the old tails from the tap and the valves, and fit new ones with the same thread and length. It’s worth replacing both at once if one is rusty or damaged.

More tap fixes: How to Fix a Dripping Tap (all tap types) · Mixer Tap Dripping? · Ceramic Tap Leaking? · Dripping Bath Tap?