triton t80si keeps not workin and tripping out?

my triton t80si only works now when the top dial is set to 'cold' setting,which is only water cold.
we always had the dial to the second setting,(dial facing down pointing to the one red line) and had the temperature on around 7. but yday morning i switched it on and trips and goes straight off, and trips the main switch located in the airing cupboard.
help please, warm shower needed!!