Triton Martinique electric shower problem, advise welcome please :-)?

Hi all I have a Triton electric shower model Martinique. In the summer I usualy have it on about setting 3 -4 for decent hot water. The other day it suddenly went red hot then freezing cold, since then I have to have it set on 8 to get any normal hot water. If anyone knows which part would have gone faulty? and were is a reasonable place to buy from? As a point of not above the heater can assembly there is 4 conections 3 with solid plastic and one a piggy back connection (with 2 wires on it). This piggy back connection had rubber sleeves on it that had been scorched/melted/burnt. It seemed the wires get hot there and the conections (from the supplier) unsuitable for the purpose. Ive repaired this, but wondering if anything could have arced out here?........Thanks in advance for any help ;-))