Shower Mixer

mitigeur de douche thermostatique

The mixer has always been a bit poor and hard to adjust.  Pretty sure I've had it apart before.  About €45 from Bricomarche 2-3 years ago.  Just recently it's almost impossible to adjust the temperature as it's so stiff, and full hot is blending in cold.  It's a common problem in the forums, and the mixer cartridge is excluded from the guarantee. I didnt look too hard, but the cheapest cartridge was around €90, and they all look pretty similar.  Castorama sell a complete thermostatic mixer at €30. Mail order from €23 + delivery.
We are 2 on a scale of 1 to 10 water hardness, 1 being soft.

The cartridge, below, is held in with 1 screw, but the scale/soap held it fast.  Luckily there are some flats that allow it to be twisted to free it, then drift it out carefully using the screw hole. Don't remove the other end as the seating washer is a critical one and didn't look common. This on/off valve shuts the output, so failed seals in the mixer will just keep leaking.

To open the cartridge put the flats near the control in the vice, then use a 24mm spanner on the flats further up.  Sadly the opening is too small for the spanner, even with a bit of filing, so the grips took care of it.

The 3 left most items (after the body), should spring out.  Mine were ceased, so carefully pressed out. Removed all the scale with emery cloth on all faces and re-assembled with a good dab of silicon. Same with the valve body.
The item to the right of the black pin has a movable, sprung plate.  This was ceased.  Freed by gently squeezing in a vice and silicon sprayed in.

On the cartridge, the end that isn't the control, is the mixed out.  The next mesh is hot, then cold. The item pushed by the spring is the thermostatic bit. Fully left, it shuts off hot & vice versa. Turning the knob to °C physically forces the thermostatic bit to cold. 

To put the temp control in the right place, turn CW ie towards cold until resistance is felt, then continue until it feels tight - its about the distance between 20 & °C  . Place the knob so the 'setting dot' matches °C . The knob should turn the opposite way to beyond 50 and to within about 5mm of °C.   

At room temperature, selecting full hot will mean the cold port is blocked.  Once the thermostatic bit gets cold eg during tests with cold water, water will freely pass from the hot inlet to outlet, irrespective of setting temp. Also, the resistance noticed above for setting the knob will go. During testing with air, noticed the hot passes to cold. Once wet, the NRVs built into the inlet stop this.

The valve does pass a little on full hot or cold, as it's just metal to metal contact on the mix bit.

Probably need to fully exercise the valve daily to stop scale forming on the thermostatic seat.

Very similar to Hudson Reed Cartouche thermostatique pour mitigeur de baignoire îlot
Référence Produit : SPN322C

July 2017. Mixer would not give full hot, so stripped and rebuild. No change, so replaced it with a Aquatrends Siena, allegedly a €48 item that Amazon had 'reconditioned' for €19 ie dented box. Overall length 259mm, a bit shorter than the old one. Ceramic disc.