Mira Sport Shower water temp problems

[Hasbo]

Hi, II've just had a new Mira Sport 9.0 KW Multifit shower fitted.

On the High setting the water is far too hot - i keep very slowly turn the dial to a cooler setting but the water stays at the same temp. then suddenly runs cold. 3 different members of my family have tried to adjust the dial to a cooler water temp., but to no avail.

On the Eco mode the water is only tepid even on the water temp highest setting.

Any ideas how to fix this please. Thanks,