The Shower Doctor Surgery: How to replace a Mira Excel

Swapping out your Mira Excel cartridge should be a relatively straightforward process once you have everything you need to do the job. To get you started, you can purchase the relevant part from our website here.

Please note this guide - and the accompanying Youtube video - is for the 903.33 cartridge, which fits Mira showers that are pre-2003. However, the newer cartridge isn't much different - so we'll explain along the way.


Firstly, disconnect everything you need to so that you don't end up causing damage to either yourself or your home. Following this, it's always a good idea to covering the bottom of your bath or shower tray. This is so when you start your work on the unit, you don't end up losing screws or other small parts down the plughole.

You don't really need many tools for the job, but the following will come in handy:

  • A cross head screwdriver
  • A pencil

Removing the existing cartridge

Using your screwdriver, undo the first few clips and remove the outer casing. The same method can also be used to get leverage under the temperature control, so just ease that out as well.

It's quite useful at this point to make a mark with your pencil on the bottom of the casing so that you can remember which way it goes on when the time comes to put everything back together.

There are three cartridges underneath. These are:

  • Green - high pressure
  • Yellow - low pressure
  • Purple

The only colour you need to worry about here is the purple one, as the other two are superseded by this.

Take out the four screws - this is when you're most likely to lose anything down the plughole so do make sure that's blocked before you start this!

When this can be taken off, you can finally get access to the cartridge itself. Note that there should be a red button on the left and a blue to the right, marking hot and cold. Make sure when you install your new one that it's not upside down and the colours are on the same side.

In terms of getting the cartridge out, it should just pull out, although if it's a bit stiff then a little rocking motion with your wrists could help.

Replacing the cartridge

Your new cartridge will come with a key, along with a position for high and low pressure. Place the key into the back of the cartridge, reset it and then set it to the high level. Don't worry if it feels a little tight - this is quite normal.

Putting the cartridges back into the brass frame is relatively simple, but one thing to be wary of is the two rubber seals on the slots of either side of the cartridge. This is the main difference between the 903.33 and the newer versions - on the latest models, there is just one rubber seal that goes all the way around the cartridge, whereas with this model they are small and of an elliptical shape.

Make sure the seals are in place and do not drop out as you put the cartridge in place. However, if this does happen and you lose the part, there should be a few spares in the pack.

You'll feel a satisfying 'clunk' as the cartridge drops back into place, and from then on it's plain sailing. Pop the screws back in and then put the outer casing back together. Line everything up, put the temperature control valve back on, turn the water on, and hopefully that's another job well done!

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