Heatre Sadia shower problem..please back?? Before I call within a plumber, my shower sytem has 3 bake...

Before I call within a plumber, my shower sytem has 3 bake settings we always use the 3rd (hot) & lately when we put it on this the wet comes out cold. Is there anything anyone recomends? We switch it on using an electric switch I'm 99% positive it's not connected to the boiler.
What is the HP rating of a Homelite...
Answers:    hail as a plumber and preferabbly those that installed it or a service rep for that model.otherwise you will void your warranty. do not be penny learned and pound foolish