The traditional mains-fed shower can be a liability. One flush of a loo or turn of a hot tap can leave you under a torrent of scalding or freezing water. Thermostatic mixer showers allow you to preset the temperature you want to shower at and then maintain that temperature — regardless of innocent, or malicious, water use elsewhere in the house.

Many thermostatic mixers can be used with pumped systems, gravity, standard mains pressure or combination boiler-fed supplies. But check with the supplier that the one you want is compatible with your water system before you buy.

There are many different styles of thermostatic mixer available but there are really only two distinct types: surface-mounted or recessed. With surface-mounted units the whole valve attaches to the face of the wall and the hot and cold pipes are either run up the wall to fix underneath the unit, or come through the wall to attach at the back of the unit. With recessed units you just get to see the controls, while the valve and water connections are concealed, normally behind a plate that’s supplied with the kit. For this feature we’ll be fitting a surface-mounted valve, but the basic principles are the same for a fitting a concealed valve.

Thermostatic shower kits cost from £80 upwards and a plumber will charge you around £100 to fit one. Follow this guide and you can get the job done in a day for free.

Tool list

  • Pipe cutters for plastic and copper pipe
  • Pencil
  • Tape measure
  • Dust sheets
  • Adjustable spanner
  • Tile drill
  • Spirit level

Materials needed

  • Thermostatic shower mixer
  • Connecting shower head
  • Plastic and copper pipe (15mm)
  • Plastic and copper connections (tees and elbows)
  • Shut-off valves
  • Double-sided tape

Step-by-step guide to fitting a shower

Check which pipe is hot and which is cold water supply; Turn off the water and drain away water in the pipes

1. Decide where you are going to take your hot and cold supplies from. If you are fitting the shower above a bath then you can tee into the tap supplies. If you are fitting the thermostatic shower to a separate cubicle you can tee into the nearest hot and cold pipes. These are often found under floorboards, or, as here, concealed in a cupboard. To check which is which, trace the pipes back from the nearest hot and cold taps. You can feel the flow of water through the pipe with the tap running. Run each tap in turn — the hot water pipe warms up very quickly.

2. Before you start work on the water system you’ll have to isolate the supply. Turn off the stopcock (often positioned under the sink) and then open the hot and cold taps to drain away the water in the pipes.

Tee into the hot and cold supplies and run the pipework towards the shower; Flush the new pipework through

3. Tee into the hot and cold supplies and run the pipework towards the shower. Check the instructions that come with the valve and make sure that you feed the hot and cold supplies to the correct sides (normally hot left, cold right). Plastic pipe is the easy-to-use plumbing solution for running under floorboards and up behind stud walls. Always use pipe inserts at joints to stop plastic pipe deforming. Include a shut-off valve on both hot and cold supplies as close as possible to the shower.We’ve found it’s easier to tighten up compression-type joints (used with these shower valves) on a copper pipe. So slot in a length of copper pipe at the end of your plastic pipe runs. Put plastic stop ends on these pipes, turn the stopcock back on and check for leaks on the new pipe runs.

4. Thermostatic shower valves can be damaged if there is any dirt in the water flowing through them. To avoid this you should flush the new pipework through. Turn the water off, remove the stop ends and ask someone to hold a bucket under the outlets while you briefly turn the water back on. Shut the stopcock off when you have finished flushing.

Mark off the amount of outlet pipe required to allow the valve to fit flush to the wall; Cut both outlet pipes to length

5. Offer up the shower valve and mark off the amount of outlet pipe required to allow the valve to fit flush to the wall.

6. Cut both outlet pipes to length. A circular pipe slice-style cutter like this works brilliantly in tight spots.

Mark off and drill the holes for the thermostatic valve; Put a collapsible olive into each inlet on the thermostatic shower valve

7. Mark off and drill the holes for the thermostatic valve. If you are drilling into tiles use a diamondtipped tile drill. Drilling into tiles creates a lot of heat so we used a kit with a water-cooled drill guide that created perfect holes very quickly.

8. Put a collapsible olive into each inlet on the thermostatic shower valve and secure by screwing the retaining nut on by one turn.

Screw the valve to the wall and then tighten the retaining nuts with an adjustable spanner

9. Align the shower valve with the supply pipes and make sure they slide into the inlet pipes fully. Screw the valve to the wall and then tighten the retaining nuts with an adjustable spanner. Make sure the shower tap is turned off and then turn the stopcock back on and check for leaks at the inlet pipes.

Connect the shower hose or riser pipe

10. The flow of mixed hot and cold water from the thermostatic shower valve is taken to the shower head either by a conventional flexible shower hose that screws into the top of the valve, or by a solid riser pipe. If your kit uses a flexible hose all you have to do now is connect it up and fit the bracket that holds the shower head in place. This kit has a solid riser pipe. It was supplied over length to suit different-height ceilings. If you need to cut your riser rail down, first measure the depth of the recess that the pipe sits in on the thermostatic valve and then on the bracket that secures the top of the riser.

Cut the riser pipe to length

11. Put some double-sided tape on the top bracket and stick it at the height you want it to be above the shower valve. Now measure between the bottom of the bracket and the top-mounting nut on the valve. Add this measurement to those you made in step ten and cut the riser pipe to this length. Cut the pipe with a pipe cutter, not a hacksaw.

Trial fit the riser pipe between the valve and bracket; Fully fit the riser and tighten the nuts top and bottom

12. Trial fit the riser pipe between the valve and bracket. Make sure the pipe is vertical using a spirit level and then mark off the top-bracket mounting holes. Drill and plug the holes.

13. Fully fit the riser and tighten the nuts top and bottom. Some kits feature an extension piece that attaches to the riser’s top bracket and takes the shower head. Fit this and then screw on the shower head. Run the shower and check for leaks. Make sure the thermostat works by switching on taps and checking that the shower temperature remains constant.

Articles like this Comments
  • mike clayton

    Hi Ben,
    Thanks for the tips, I’m nearly ready to start! Everything I’ve read has stated you must run cold fed from water tank, this is OK but a major problem for me. I’ve read the instructions on the shower valve I bought from B+Q and it states this valve is suitable for unbalanced supplies i.e. main fed cold and tank fed hot. Does this sound right as it will save me a load of work.
    I was also going to fit a pump becasue my hot water is level with the shower, If I connect to the cold mains, obviously I will not need to pump it, so can I purchase a pump that only pumps hot water??

    Look forward to hearing from you
    Regards Mike

  • Anonymous

    There are 4 pipes coming from the controls why 4 not 2 ?

  • NIEL

    Ihave fitted a thermostatic shower over the bath and plummed into the hot and cold suypplies to the bath. I have switched on the shower and the flow is very poor. I believe i need a pump but which type and is it easy to fit.

  • Samuel Joy


    These previous ‘Ask the Expert’ Q&As may be of use to you

    Hope they’re useful

    Sam Joy (Online Editor)

  • Samt223


    I’m about to upgrade my bathroom and was wondering if I should tile before I fit a new mixer shower, or is it easier to tile around the shower? :o)

    Many thanks.

  • Charwell

    Hi Ben,

    Does in matter if the hot water inlet is on the right (even though guide to shower valve says always ensure it is on the left hand side).

    Showers seems to working although temperature control is in reverse.

    Plumbing in my shower has been done by someone else so difficult to change round behind the stud wall and tiles.

    Any advice.


  • Anonymous

    hi , can someone help me i have brought a arm extender to put my shower hose into but i have been told that the extender is for a ridged shower hose and mine is a screw in is there any way i can connect it with a connector or some thing (hope this makes sense), 🙁

  • Robert Bowmer

    I’ve fitted my shower but the Shower Doors keep opening on there own. Any quick tip to keep them shut?

  • A plumber

    Run a tiny blob of clear mastic(whilst the bath is full)under where the door is situated. Always works for me..

  • A Potter

    Hi, The white sealant running around the base of our shower seems to be old and is possibly not as ‘sealed’ as it has been (there’s wafer thin gaps where the sealant should touch the shower/tiles). Everything is still there and in place, but I’m concerned that a bit of water is getting through each time we shower. Does it need fully replacing so is there an easier fix?

  • Tim Ford

    Some of the items that also forgotten when replacing a shower is the shower door, check out for all you shower doors and valves.

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