My triton T80si electric shower extremly hot and luke warm?

My Triton T80si Electric Shower is either extremly hot (setting 7 above, or luke warm 6 or below) on both settings. You just can't get the right temp. The low presure light does not come on at all and i live in a soft water area. Do you think that this is a thermostat problem? Flow/Stabilizer valve? The household water pressure is good, and this happens even when the heating and washing machine etc are all off. Any ideas as this has just started?