Shower - twist control knob is stuck

Ant555

I have a shower where one of the controls seems to be stuck.

The temperature side is OK but the left side is the on off/ divert between the top shower head and hand held and this only works for the overhead shower, It simply will not twist towards me for the hand held unit.

I can see youtube videos  on replacing temp flow cartridges but does anyone have any thoughts if a mixer control on a shower bar is serviceable/fixable by a basic DIY'er or is it easier to get a new shower and fit - A like for like replacement probs £120 parts.

Its this shower
 https://www.victorianplumbing.co.uk/premier-thermostatic-bar-valve-and-shower-kit-jty386

Rodders53

The maker's website https://www.nuiebathrooms.com/products/showers/complete-shower-sets-round/?col= may have the installation manual which can sometimes include maintenance info.
If not ask them?

But you could:

Turn off water H&C. Release pressure by opening overhead and sink taps.
Then remove the handle on the control.
That'll expose the valve itself.
Undo with a suitable spanner and clean up the seats, any filters etc.,. of limescale.
A dab of silicone grease on any rubber seals and reassemble. 
Test mechanical operation dry.
Then close all taps and turn on H & C.
Finally test wet.