The water temperature from my mixer is too cool, what can I check?

Check that the hot water temperature at basin taps is acceptable (this should be approximately 55 to 60°C). If it is not, then the thermostat on the hot water system (e.g. hot water cylinder or combination boiler) needs adjusting.

Check whether the showering temperature is acceptable by pressing the 'maximum temperature stop' override button (if fitted on the mixer) and increasing it to a higher setting? If it is then you can reset the 'maximum temperature stop.  If these steps don't work, then we would have to inspect the shower valve and check the thermostatic cartridge