How to install a thermostatic mixer shower

How to install a thermostatic mixer shower

Jeremy, construction site supervisor, Cardiff

Guide written by:

Jeremy, construction site supervisor, Cardiff

134 guides

Whether you're setting up a new system or replacing an old one, installing a mixer shower should be a straightforward task. Used to provide your shower head with a steady flow of hot water, thermostatic shower valves are usually installed on connectors which are concealed by plates. Read on for our step-by-step guide.

Important features

  • Preparing to install
  • Pre-assembling your thermostatic mixer
  • Installing the mixer shower
  • Connecting the shower hose and head
  • Turning on the water and testing the mixer
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Whether your bathroom is fitted with a walk-in shower, a shower enclosure or a shower over a bath, your shower should have a decent flow rate with a consistent and easily adjustable temperature. The best way to achieve this kind of user comfort is with a thermostatic mixer shower. It's important to note, however, that thermostatic mixers are not compatible with instantaneous water heaters and can only be used with storage water heaters such as direct water heaters (hot water cylinders). If you do have an instantaneous water heater, a shower mixer with an anti-scald feature and flow regulator will be your best option. Dual-tap mixer valves are not economical or comfortable to use, and are therefore not recommended for showers.


  1. Preparing to install
  2. Pre-assembling your thermostatic mixer
  3. Installing the mixer shower
  4. Connecting the shower hose and head
  5. Turning on the water and testing the mixer

Required skills

As most fittings are standard in size, you will generally just have to screw them in using a spanner (after applying PTFE tape or even oakum and putty). In older systems, the connections are often soldered. In this case, you will have to install compression fittings to adapt the system to your new mixer valve. No matter what you're dealing with, installing a thermostatic mixing valve should be easy, just as long as you are careful and use the right tools and materials.

Completion time

Approx. 45 mins

Number of people required

1 person

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Adjustable spanners

Turning off the water and identifying the fittings

First of all, isolate your water supply and turn on the closest tap to drain the pipes.

Refer to your instructions for a general overlook of the parts you're working with and identify your hot water feed (this will usually be on the left).

Next, make sure that, once you've dismantled the old valve, that the fittings on your water feed will be compatible with those on the new shower valve. These fittings generally have a standard thread size (1/2 or 3/4 BSP). If everything is compatible, then great! If the female connectors at the water inlets are not the right size, you will have to install some reducer fittings. These screw-in fittings are installed with PTFE tape and allow you to connect two fittings of different sizes.

Replacing an old system using compression fittings

If you don't have the right fittings in place and have to cut your old soldered pipes to install the new tap, you will have to install compression fittings to connect your copper tubes to a threaded fitting (without any further soldering). To do so, you will have to complete the following steps

  • cut your copper pipes down to size with a metal saw;
  • deburr and clean the end of the copper pipe;
  • measure the pipe diameter;
  • insert the nuts, olive and the threaded male part of the fitting;
  • tighten everything using the appropriate spanners.
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PTFE tape

You will have to check and adjust the various parts of your thermostatic mixer by completing a test run (or pre-assembly).

  • Screw in the z connectors so that they protrude around 40 mm from the wall; refer to the instruction manual for the exact measurements.
  • Screw the escutcheons or cover plate into the wall.
  • Adjust the assembly by screwing or loosening the fittings until you achieve the exact distance between the fittings as specified in the instructions (usually a gap of 150 mm between the centre of each fitting).
  • Check that everything is level by placing a spirit level onto the escutcheons or cover plate.
  • Install the thermostatic mixing valve, turning the nuts by hand. Be sure to check that the nuts aren't touching the escutcheons. If this has happened, adjust the depth of the z connectors by screwing or unscrewing.
  • Once again, check that everything is level using a spirit level. If everything is in order, dismantle the assembly making sure to measure and note down the exact distance between the z connectors and the wall.
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Thermostatic mixer taps

You can now proceed to assembling your mixer shower.

  • Seal your z connectors using PTFE tape; always unroll the tape following the direction of the thread.
  • Tighten the z connectors into the same position as before using your measurements and an open-ended spanner. Make sure that the position matches up with your measurements from the previous step (depth and distance between fittings).
  • Check that everything is level using a spirit level.
  • Lay a silicone seal around the z connectors and screw in the escutcheons or cover plate.
  • Be sure to check that both ends of the mixer are equipped with inlet filters, paying special attention to ensure that they are positioned the right way around.
  • Screw the mixer onto the z connectors using an open-ended spanner (there is no need to use any washers). If everything is correctly assembled, the nuts should not be touching the escutcheons.
  • One final time, check that the mixer is level and correct this as needed.
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  • Check that there are rubber washers in each end of the shower hose.
  • Screw the shower hose onto the mixer firmly by hand. If the shower head is not attached to the hose, repeat the above procedure to connect it.

Do not use any tools to tighten these parts.

Now that everything is connected and properly tightened, you can now turn your water back on. Make sure your mixer valve is in the 'off' position. If nothing leaks, this means your installation is watertight.

You can now try out your mixer and shower head by testing the various flow rate and temperature settings.

Depending on the model, you may have to calibrate the valve to set the temperature. To do so, grab a thermometer and refer to the instructions. Adjust the setting screw until the right set temperature is achieved (this is usually factory-set to 38°C).

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Shower heads

Tools and equipment

  • A thermostatic mixer with fittings and washers
  • A shower head and hose (with washers)
  • A pair of escutcheons (optional)
  • A set of z connectors
  • Two compression fittings and/or reducers (if required)
  • Silicone and a skeleton gun
  • PTFE tape
  • A set of open-ended spanners or an adjustable spanner
  • A spirit level
  • A straight edge
  • A slotted screwdriver
  • A thermometer (if you have to set the temperature)

Personal protective equipment (PPE)

  • Work clothes
  • Protective goggles
  • Protective gloves

Please note: this is a non-exhaustive list; be sure to match your personal protective equipment to the job at hand.

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Adjustable spanner

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Guide written by:

Jeremy, construction site supervisor, Cardiff, 134 guides

Jeremy, construction site supervisor, Cardiff

Electrician by trade, I first worked in industrial estates where I installed, wired and fixed a large number of electrical installations. After this, I managed a team of electricians for this type of work. 10 years or so ago, I turned to building and construction. From the modest family home, to gyms and theatres; I have been able to coordinate, audit and organise all sorts of construction sites. for 4 years now, I am restaoring and bulding an extrension to a bungalow in the heart of the welsh countyside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electricty, anything goes! We have, my wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions, and to orientate and advise you on coosing your tools? Easy!

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