Shower tap help

[Derek88]

Hi guys, I have a problem with my temperature tap on the shower. There is a little red piece come out and it is stuck on hot and I don't know how/which way it goes in. I have had the tap off and I'm struggling to find what it's purpose is. I have added some pictures with the problem and make of shower
Thanks in advance

 

[terryplumb]

Its purpose is to provide a physical stop,to prevent the selection of higher temperature range ,unless the red button is pressed in first. So when turning the handle to increase temperature ,it comes to a point where you can't turn any further ,unless red button is pressed in.
If you can still turn the silver handle ,and select a temperature range suitable for you to shower ,and still alter it to make it cooler or warmer,should you wish to do so,then you don't need to worry too much about refitting the red bit. However ,if elderly ,or young children ,or mentally challenged people have the use of this shower ,then you should replace it.

 

[Derek88]

Is it not fixable? It doesn't turn at all

 

[terryplumb]

Possibly ,depends on what caused it to come apart ,which parts need sourcing and replacing. Personally ,I don't get involved in trying to repair that type of shower valve ,it's not cost effective for the customer to pay for my time involved. It takes ten minutes to fit a new valve ,and can be purchased for around £60. You can swap it yourself in ten mins ,and all you need is a spanner to undo the two nuts .