What Is Wrong With My Halstead Ace High?

My Halstead Ace High Will Not Switch Off When I turn Off Hot Water And When Left To Run It Will Heat Up The C/Heating Both Micro Switches Are Working ,Does Anyone Know If It Could Be Something seized In The Group Set As This Was The first Time It Was Switched On , There Is Also A small Dribble Of Rusty Water From Behind The Lower Micro Switch (I Have Cleaned Switch ) Any Ideas Would Be Appreciated ,Any Idea Of Cost Thank you