I fitted a new Mira Sport 10.8 kw sho...

I fitted a new Mira Sport 10.8 kw shower heater tank yesterday with the adaptor kit as the old unit had given up and according to the test you need to carry out on the old tank to determine the fault it pointed to the heating element in the tank had blown as the unit would not produce any hot water on on all three settings.When everything connected and turned on the unit did not produce any hot water at all on all settings and on medium and high settings the overheat light comes on!!Can you please help I'm confused!!!!!!!