Aqualisa power shower?

I have an aqualisa power shower that only works on boost. Is this due to the mico switch that sits behind the on off ring? I have looked at it and the little switches seem ok, however one of them does click each time you push it but one doesn't. I assume this may be the fault? If so replacing the switch may cure the problem? Also the temp control mixer unit sometimes makes a grinding noise when u turn the heat up. Pump runs fine and quiet. Any help please?