Thermostatic shower not getting hot enough

[Maisie's dad]

Hi there

could anyone help me to work out why a thermostatic mixer shower fed by mains cold and tank hot isn't getting as hot as it used to. I've tried turning the cold pressure down a bit but then the entire shower pressure is not great.
Any ideas please?
Thanks in advance

 

[ChrisR]

How did you "turn the cold pressure down"?
Is the mixer designed to work off unbalanced (completely different pressure) supplies?

 

[Maisie's dad]

Hi there thanks for the reply. There are separate supplies the cold had a tap on it and I turned it down. The shower became hotter but the flow was slower

 

[Maisie's dad]

Sorry also the mixer is a £99 job from Wickes (now discontinued I believe)