In this article, we explain how to change the thermostatic cartridge (451.71).


The Mira Excel range is one of the UK's most popular mixer showers; it's the favourite choice by consumers and installers alike. As such, we receive lots of requests asking how to replace thermostatic cartridges in the Mira Excel models (2006 - current).


Our video below highlights the process involved in replacing the thermostatic cartridge of a current Mira Excel EV thermostatic mixer shower (2006 - current). (Older Excel models use a different cartridge (903.33) that isn't explained in this article.)


Built-in (recessed) valves should follow a similar procedure but may differ slightly. As always, you must follow all safety guidelines or consult a trained plumber.


The products mentioned and/or shown in the video include:





From our video, general instructions are as follows for changing a Mira 451.71 thermostatic cartridge:



  1. Remove the temperature control knob, flow lever assembly and cover shroud on the front of the shower valve. The latter may require a bit of encouragement to detach.
  2. The current/old cartridge should be held into place with 4 screws. Undo these, taking note that the "red" hot side is on the left and the "blue" cold side is on the right. A good tip would be to cover the plug hole before removing these screws, in case they accidentally fall down the drain. Replacement scews (Mira 451.77) can be bought together as a pack if needed, though.
  3. Pull the current/old cartridge out. You may need to wiggle it gently in order to pull it out completely.
  4. Remove the old, large seal as well. This may be found on the back of the cartridge that was just removed, but could also be left in the valve body.
  5. Inspect the 2 filters inside the valve (one on left and right). Clean gently if needed and then place back in. These can be taken in/out with long-nose pliers to make it easier. Alternatively, the filters can be replaced with the new ones provided with the new cartridge.
  6. Using the silicone grease provided, apply a liberal amount onto the hot/cold seals on the back of the new cartridge, as well as the seal on the face of the body (see video).
  7. Push the new cartridge into place until a slight click is heard. Remember, the "red" hot side is on the left and the "blue" cold side is on the right (as you look at the shower).
  8. Secure the new cartridge with the 4 screws from Step 2.
  9. Reattach the cover shroud, flow lever assembly and temperature control knob.
  10. Ensure the shower is in the off position (lever facing downwards) before turning the water supply back on and testing. Inspect the underside of the shower body to ensure no leaks from the new cartridge appear underneath.           

               How To: Change a Mira Excel thermostatic cartridge (451.71) image 1 - A close up of the Mira Excel thermostatic cartridge assembly (451.71), as shown in the video.

A close up of the Mira Excel thermostatic cartridge assembly (451.71), as shown in the video.



If you find that the temperature of the new cartridge isn't to your liking (for example, it isn't hot enough), see our guide on adjusting the temperature of Mira Excel mixer showers.