How to replace a thermostatic shower valve yourself

By Benjamin Clarke | Published on 20th July 2021

If you've got a few tools and have had a go at a bit of plumbing work in the past before, then replacing a thermostatic shower valve is not the most difficult DIY job to carry out. In this article, we'll run you through the steps of replacing an exposed shower valve.

If you've got a hidden shower valve that's concealed behind a wall or tiling, that's going to be a little more complicated and beyond the scope of this article. This might be worth getting in a professional.

1. Do your checks

Most thermostatic shower valves are installed in a standard way, with standard measurements. Assuming your valve passes the following checks, you can continue and get on with the job. If not then things aren't as straightforward and you may be better calling in a plumber.

Check that:

Your hot water supply is on the left and the cold on the right
The centres of your valve connectors are spaced at 150mm
The projection from the wall to the front of your connectors is about 35 - 40mm

2. Turn off the water

You don't want to start unscrewing and dismantling things before you've stopped water flowing into your shower as this has the potential to be dangerous and cause damage.

Somewhere in or around your bathroom will be some isolation valves for the hot and cold water supplies that feed your shower valve. Locate these valves and turn them off. If you don't have isolation valves (or you can't find the) then turn off your mains water supply at the stopcock.

3. Remove existing pipework

Your new thermostatic shower valve will probably come with with its own solid, riser pipe which means you'll need to remove the existing one, assuming your current shower has a riser pipe.

Riser pipes are normally attached to wall with a couple of brackets so you can unscrew the bracket to remove the pipe. If you can't initially see any screws, they may be hidden behind a little plate that you should easily be able to pop off to expose them.

4. Remove existing shower valve

You should now be free to go ahead and take out the old shower valve. If you look at the hot and cold feeds, you should see two large nuts that attaches the valve to the feeds. Undo both nuts while holding the shower valve at the same time. This will help to ease it gently away from the wall without it falling on the floor.

You can then remove the covers from the supply pipes, cleaning off any dirt or grime that has built up on the wall.

5. Flush out the pipes

It's a good idea to run water through the exposed pipes just in case any dirt or debris has built up and needs flushing out. Switch on the water again and run the hot and cold feeds for a few seconds.

Depending on the location of your isolation valves or stopcock, you might find it easier to get another person to help you. You might also want to use a bucket to catch the water and avoid making a mess.

6. Install the new shower mixer valve

The first thing to do is to it the new covers over the supply pipes. They should just screw on and should be tightened until they fit flush against the wall. You should adjust them to make sure they're level and can even use a spirit level if you want to be absolutely precise.

Into the back of the valve you should fit the accompanying seals (or filters) that waterproof the valve, and you can then press the valve in place and tighten up each nut. You want the nuts to be tight enough so that the valve is secure against the wall, but be careful not to tighten them too much as you risk damaging the waterproof seals. Make sure you're putting on the valve the right way round and check, as you did originally, that you've got hot on the left, cold on the right.

7. Install riser pipe and brackets

Hopefully you'll be able to use the same holes for fixing your new riser pipe and brackets to the wall. There's not a great deal of variation when it comes to riser pipe sizes, so it's likely you can use the same holes. If not, you'll need to take measurements and drill some new ones.

You'll probably have a diverter valve that screws into the top of the body of the new thermostatic mixer valve. Assemble the riser pipe and attach it to the diverter valve and screw it up to connect. Screw in the brackets to ensure the riser pipe is held in place securely. You can hen fix the new shower head to the top of the riser pipe. If there is a body wash attachment, then attach the smaller showerhead and hose too.

8. Test your shower and valve

Turn your water back on and switch on the shower. Look for any leaks around the valve or shower head. Small leks might just indicate that you need to tighten some connections and the leaks should stop once this has been done.

You also need to make sure that the temperature of the water is correct and runs up to a maximum of 38°C. The best way to do this is using a thermometer and holding it under the flow of water. If the water is not 38°C then you'll need to pull off the thermostat head to access the cartridge. With the water running, adjust the cartridge accordingly to get 38°C. Once you're happy with the temperature, you can replace the thermostat head and get on with having a shower.

View our thermostatic bath and shower valves

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