Immersion heater trouble

Hi, I would be grateful for any advice.

My hot water system at home consists of peak and off peak immersion heaters. I replaced the ‘peak’ immersion heater around a year ago as the old one had blown. We leave the ‘peak’ switch on 24 hours a day. It has been fine up until a few days ago when I noticed a ‘fishy’ smell coming from the cupboard where the hot water cylinder is. Then had a shower yesterday morning and noticed that the water was luke warm. Took the switch off the wall and noticed…

Immersion heater trouble