Triton Madrid ll 8.5 kW shower?

Power set on economy setting. Water cold untill i turn temp down to approx 6 ( lower water pressure ) and you can hear a click (heating element coming on ) Water slightly to hot. If i turn temp knob to 6 (More water flow ) You can hear a click and the water goes cold. Shower has worked ok for 26 months and now this is happening.I would have thought it should work completely opposite to this ie Flow pressure there, turn power to economy Element switches on. Reduce flow till you get right temp. Does anyone know what is causing this problem