As a standard immersion heater is 3KW, so it would take 2 hours to heat 100 Litres of water. After an hour and a half, it will only have reached about 53 degrees.....
Podiatrists cite Plantar Fasciitis as being the most common cause of heel pain. Typical symptoms of this condition include sensations of pain, burning or heat in one or both heels.
Heel pain is usually caused by a walking stride that exerts excessive stress on the heel bone. Discomfort can also result from poorly made shoes, obesity, a stress fracture of the heel bone, bruises of the fat pad under the heel, or a disease such as rheumatism or gout.