Shower valve cartridges: leaks, wandering temperature, and matching the part

A shower that drips after you turn it off, or runs hotter and colder while you stand there, is often blamed on the cartridge. Sometimes that is right. Sometimes the valve is scaled, the supplies are uneven, or the shower is a different type entirely. This page is about telling those apart, and about buying a part that belongs to the valve on the wall. We are not printing part numbers. On 14 November 2026 we did not find a Wickes page for a replacement cartridge that said which valves it fits, so there is no product link here.

Manual mixer, thermostatic mixer, electric shower

A manual mixer blends hot and cold in the proportions you set. If someone runs a tap, or the boiler's flow changes, the temperature can move, because the valve is not correcting it.

A thermostatic mixer is meant to hold the temperature you chose. Many bar valves are this type. They still have a cartridge or a thermostatic element, and they still fail. What that kind of valve is for, including the bath limit in the Building Regulations, is in thermostatic mixing valves.

An electric shower is neither. It heats cold water in the unit on the wall. There is no hot-and-cold cartridge, and the inside is electrical. See electric showers and mixer showers. Do not open the unit to look for a cartridge.

What the symptom is likely to be

This is a way to describe the fault, not a diagnosis from the hallway.

• The head drips for a minute, then stops. Often the hose draining. Not a cartridge.
• It drips for hours, or the valve body weeps. The shut-off is not sealing: a worn cartridge, a seal, or scale. Dry the pipe joints first. A drip there is a connection, not the cartridge.
• The temperature moves when another tap runs. On a manual mixer that can be normal. On a thermostatic valve it can mean the element is no longer compensating, or that the supplies are further apart in pressure than that model allows.
• It will not get hot, or it runs cold after a minute. On a combi, the boiler may be limiting the flow. On a gravity system, the head of water may be too low. See low water pressure. Scale can do this too. See limescale.
• The handle is stiff or gritty. Scale, or a failing cartridge. Forcing a thermostatic handle can break the plastic inside it.

A valve that has always done this may be the wrong valve for the system, not a failed part. The maker's instructions state the pressures for that model. We are not repeating them, because they differ.

Isolate first

Turn the shower off at its handles. Then shut the water to the valve.

Many mixers have small isolating valves on the hot and cold pipes, in the wall, above the ceiling, or in a cupboard behind. A slot or lever across the pipe is closed. Isolation valves covers the ones that will not turn. If you cannot find them, use the stopcock, as in find a leak and the stopcock. Do not remove a handle while both supplies are open. A cartridge that comes out under pressure will flood the tray.

If the pipes disappear into a tiled wall and there is no isolation, access alone makes this a plumber's job. Do not chip tiles off to look.

Match the make and model

Shower cartridges are not a standard size. A cartridge from another maker, and often from another range, will not fit. Ordering because it "looks about right", or by a number from a different model, is how people buy a part they cannot use.

Before you ask a merchant or the maker, collect the name on the valve or the faceplate, the range if it is printed or in the booklet, whether the valve is exposed or concealed, and a photograph with the handle still on. The maker's spares diagram is the document that names the cartridge. If the name has worn off, a plumber who knows the range is more useful than a guessed code.

We are not printing part numbers. A number we had not taken from the valve, or from a page that states which valve it fits, would be a guess. Wickes search on 14 November 2026 returned whole shower valves, radiator valves and unrelated filter cartridges. None of those is a spare for the valve you have. A complete new valve is a different decision: the pipes, the wall and the system all have to suit it.

Whether the valve is an exposed bar or concealed in the wall changes how you reach the cartridge. See bar vs concealed shower valves.

Scale, and when to stop

In a hard water area, scale can make a thermostatic valve stick or drift. Some makers sell seals rather than a whole cartridge, and some say the cartridge can be cleaned. Follow that model's instructions. Do not soak a thermostatic cartridge because a shower head can be soaked. The element is not a nozzle.

Stop and call a plumber if you cannot isolate the valve, the body is cracked, water is coming from inside the wall, you are unsure the valve still suits a pumped or gravity system, the shower is electric, or a cartridge from the maker does not cure it. A thermostatic valve that has been apart should be checked before anyone who might not react quickly to hot water uses it. Commissioning is on the thermostatic mixing valve page. We do not give a temperature to set.

Basin and bath mixers use cartridges too, but they are a different spare. See mixer and bath taps and dripping taps.

Can I buy a universal shower cartridge?

Not in any reliable sense. It has to match the make and model. If the name is readable, use the maker's spares information. If it is not, a plumber is more likely to identify the range than a generic listing is.

The temperature moves when the kitchen tap runs. Is that the cartridge?

On a manual mixer, the valve is not designed to correct for that, so a new cartridge may change nothing. On a thermostatic valve, it should cope with ordinary changes. If it no longer does, the element may have failed, or the pressures may be outside what that model can handle.

Do I have to turn the stopcock off?

You need the hot and cold supplies to that valve closed. Local isolation valves are enough if they hold. If they do not, close the stopcock. Do not remove the cartridge with the supplies open.