Bath shower mixers and diverters: how they work and common faults

A bath shower mixer is the tap on many UK baths that fills the bath from a spout and also has a hose and handheld shower. The part that switches the water between the two is the diverter. When it works, you barely notice it. When it wears, water dribbles from the spout while you shower, or the shower drops back to the spout halfway through a hair wash.

This guide explains how the diverter works, the faults you are likely to meet, and what to do before swapping a mixer like for like.

How a bath shower mixer works

Most bath shower mixers in UK homes sit on the bath deck in two tap holes. Hot and cold come up through the tails into the body, where two handles or a single lever control how much of each goes in. The mixed water then goes to one of two places:

• The spout, to fill the bath.
• The hose and handset, for a shower.

The diverter decides which. On many mixers it is a knob on top of the spout or the body that you pull up or turn. Others have a push button, a lever or a turning dial. Wall-mounted exposed mixers work the same way, with the body on the wall instead of the bath deck.

Many bath shower mixers are not thermostatic. They mix hot and cold by hand, so a change in pressure on one side, such as a toilet flushing, can change the temperature. If that is a problem, see thermostatic mixing valves. A shower valve built into the wall is a different kind of fitting, covered in bar vs concealed shower valves.

Common diverter faults

Water from the spout while showering. The diverter is not closing the spout fully. Often the seal inside is worn or limescale is stopping it seating. Some water from the spout is a common sign of an ageing diverter.

The diverter drops back to the spout. Many pull-up diverters stay up because the water pressure holds them. If pressure is low, or drops when someone else uses water, the knob may fall back. That can be a feature of the design on low-pressure systems rather than a fault. If you have low pressure throughout, see low water pressure.

The diverter is stiff or will not move. Limescale is a common cause in hard water areas. Do not force it, as the parts are small and can snap.

Leaks at the hose. Drips where the hose meets the mixer or the handset usually mean a worn washer or a tired hose rather than a diverter fault. Shower heads and hoses covers swapping these.

Drips from the spout with the taps off. That is the tap valves, not the diverter. See dripping taps and mixer and bath taps.

Some makers sell replacement diverter parts or cartridges for their mixers. Whether one is available depends on the brand and model. Check the maker's documents for your mixer before buying anything.

The hose and backflow

A handheld shower on a long hose can reach into a full bath. That matters because the water regulations are concerned with dirty water being drawn back into the supply. Water Regs UK's bathrooms page says all water fittings in a bathroom must be supplied via appropriate backflow protection, and that the local water company decides what is required. It also notes that a single-flow mixer tap needs single check valves on the pipework supplying it, in addition to the gap above the bath.

We do not say which arrangement your bath needs. Follow the mixer maker's instructions, and see check valves and backflow for the general idea.

Isolate before a like-for-like swap

If you are replacing a deck-mounted bath shower mixer with a similar one, the job starts with turning off the water.

• Isolation valves. Many baths have an isolation valve on each tail, behind the bath panel. Turn the slot a quarter turn so it sits across the pipe. Bath panels and traps covers getting the panel off without damage.
• No valves, or valves that will not shut. Turn off the stopcock and, on a tank-fed system, the valve on the feed from the cold water tank. See find a leak and the stopcock.
• Drain and cool. Open the taps to drain the pipes, and let the hot side cool first.

Then check the new mixer matches the old: the same tap-hole spacing, suitable for your water pressure, and connections that fit your pipes. Follow the maker's fitting instructions.

Do not try a like-for-like swap if there is no clear access to the pipes, if the mixer is built into a wall or a tiled panel, or if the bath would have to come out. That is a job for a plumber. If your shower is pumped or electric, leave anything electrical to a qualified electrician.

A mixer Wickes lists

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

Why does water still come out of the spout when the shower is on?

The diverter is usually not sealing the spout fully, often because of a worn seal or limescale. A small amount is common on older mixers. If it is getting worse, look for a replacement part from the maker or consider a new mixer.

Why does my shower switch back to the bath tap?

On many pull-up diverters, water pressure holds the knob up. If the pressure drops, it falls back. That is common on low-pressure systems. A plumber can tell you whether a different mixer would suit your supply.

Can I replace a bath shower mixer without removing the bath?

Often, if there is a removable bath panel and space to reach the tails. If the pipes cannot be reached, or the bath is boxed in or tiled, call a plumber.