problem

Hi My daughter has a Grohe mixer shower (see photos) and however I try to mix it to warm / hot it only just manages slightly warm or cold. I don't know how old it is as it was already fitted when they moved in. Can anyone suggest what might be the problem. Other showers are fine so I think...

The frost freeze faucet() seemed clogged and I was unable to unclog it like I did last time. It hasn't been used for a few years, so I suspected hard water build up. Last time, I simply took it off and cleaned it (when I first bought the house, I haven't really needed to use it so it went unused...