I have recently had an "Embrace" Thermostatic Mixer Shower fitted . There is a separate control tap for water and temperature. I have a combination boiler with 1 bar pressure which is compatable with this shower. The problem is , when I turn the tap to regulate the temperature I only get two extremes, either very hot which would take a few layers of skin off or freezing cold. It is impossible to get a happy medium. Any ideas on what the problem is?