How to Replace a Shower Mixer Tap: The Complete Step-by-Step Guide

A shower mixer that drips, spins in a vacuum or refuses to regulate the temperature always ends up becoming unbearable. Replacing it is a plumbing operation within the reach of a careful DIYer, provided you respect the order of the steps and choose a compatible model. This guide accompanies you from the choice of the unit to the final test, with the tools you need and the precautions for not damaging the fittings.

The tools and materials you need

• An adjustable wrench or water pump pliers to loosen the nuts
• A flat screwdriver and a Phillips screwdriver
• An Allen key (often 4 or 5 mm) to remove the handle
• A clean cloth and fine abrasive paper
• Jointing compound or PTFE tape
• The new mixer, a socket and its new hose

Before starting: turning off the water supply

The first thing to do is turn off the water. Find the stop valve of the home, usually located under the kitchen sink or near the water meter. Close it by turning clockwise, then open a tap in the home to bleed the residual pressure. Check that a tap stays closed: if the water no longer runs, you can work safely.

Dismantling the old mixer

1. Remove the handle with the Allen key by loosening the hidden screw located behind or underneath.
2. Remove the escutcheon (the decorative piece that hides the wall connection) by pulling gently towards you.
3. Place a container under the fittings to catch the residual water.
4. Unscrew the two fixing nuts with the adjustable wrench, holding the opposite fitting to avoid twisting the pipe.
5. Pull out the body of the mixer and clean the threads with the cloth and the fine abrasive paper.

Choosing the right model and the right fittings

The centres (distance between the two water supplies) are standardised: modern mixers install on 150 mm centres. However, check whether your wall outlets are spaced 150 mm or 130 mm apart, in which case you will need adapters. Prefer a model with a ceramic cartridge, more reliable and more precise in temperature regulation, and check that the threads are 3/4 inch or 1/2 inch depending on your pipes.

Fitting the new mixer

1. Wind 5 to 6 turns of PTFE tape in the direction of the threads, or apply a thin coat of jointing compound to the fittings.
2. Screw the nuts of the new mixer on by hand to find the correct alignment, without forcing.
3. Tighten each nut alternately with the adjustable wrench, without excess, so as not to crack the brass.
4. Put the escutcheon back in place and retighten the handle screw with the Allen key.
5. Connect the shower hose and its hand shower, checking that the O-ring is correctly positioned.

The mistakes to avoid

• Forcing on the nuts instead of freeing a seized thread with penetrating oil
• Forgetting to swap hot and cold water on a mixer without an anti-scald mechanism, which reverses the handle
• Tightening by feel without using PTFE tape, which causes leaks on the fittings
• Throwing away the original hose before comparing its length with the new one

The final test and the temperature balancing

Slowly reopen the shut-off valve, watching the fittings for a minute. Check the seal with a dry cloth passed over each joint. Then open the mixer fully in the cold position, then bring the temperature up gradually. If the handle stops too early or too late on the hot setting, remove it and recentre the temperature limiter according to the manufacturer's instructions.

A cleanly replaced shower mixer lasts about fifteen years. By following these steps, you avoid leaks and enjoy a stable temperature. If a leak nevertheless appears after the test, tighten the connecting nuts a quarter turn: in the vast majority of cases, the problem comes from a badly positioned gasket, not a fault in the mixer.