Repairing thermostatic shower cartridges

[opps]

A friend has a Crosswater cartridge which is now obsolete.

His goes from pretty cold to boiling hot. It is really difficult to find anything in between. Turn the knob by about 2 degrees and you either freeze or burn.

It has been dipped in Oust limescale cleaner for about 40 mins.

Is it possible to repair them? How do they actually work? It looks as though the cartridge can be dismantled.

 

[ianmcd]

call shower doctor

 

[MeldrewsMate]

Has your friend ever had the shower working properly?
Could it be that the hot and cold water connections are incorrect?

If it has once worked correctly then it may be that the cartridge shuttle (the movable bit inside) is sticking. The symptom would be a shower which alternates hot and cold with no further input from the user. Look carefully and you may see where the cartridge dismantles, but first try a descaling solution if you're not mechanically competant.

BTW, it is possible to be SCALDED by a hot shower, but certainly not burned.