why should the hot water from my shower be tepid compared to the heat of my bath hot water ?. I have a condensing boiler in the kitchen, and a hot water tank /immersion heater upstairs and a cold water tank in the loft. i think shower unit above the bath is gravity fed.
There are pins that can be put in the shower controller to stop by accident it getting too hot. Often there is a button to allow you to over ride it. Maybe you have pin in too low of a setting?