If your hot water is not working then its either the Thermostat or Element (I am a spark by trade) On your hot water tank you should have Two elements with self contained stats ,one is for Economy 7 and the other is for the Immersion . I will bet fatburys left bollock that one or more of the elements is fucked ,they should last 5-10 years .
please be wrong
I did have a plumber out, and he tested the elements. He said nowt was wrong with them!