Once upon a time, before gas central heating came out. People used coal fires to heat their homes or coal fire central heating units but they also had immersion heaters as a source of hot water. Im sure some on here remember those days. Now correct me if im wrong, but did people only use the emmersion heater when they wanted warm or tepid water for a bath?
..........errrrrrm NO!! I believe they were used to get HOT water. Gas boilers only replaced these as they were more efficient at heating the sater as and when instead of storing a huge quantity of hot water.
Ok im biased, but if people honestly dont know how to produce very hot water in their tanks (especially due to being tight fisted) with emmersion heaters than something is drastically wrong with them.