Shower mixer cartridge stuck

[InvictusBob]

We have a Mira Excel mixer shower in our spare room. The max temperature seems to have recently stuck at lukewarm. It works fine between cold and lukewarm! The shower is rarely used. As a new cartridge looks like costing me around £100 I'm keen to know if there is something I might do to fix it - drop it into boiling water?, put it in the freezer?, soak it in a limescale treatment?, drop it from a great height?

 

[ChrisR]

Soak it in a mild descaler, but that's the way they do fail eventually.

 

[InvictusBob]

Thanks for that, I'll give it a try.