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 Spurs. Another common cause of heel pain is heel spurs. A heel spur is a pointed bone fragment that forms on the heel bone and can often develop in conjunction with plantar fasciitis. Similar to plantar fasciitis, heel spur pain is most noticeable when walking after periods of rest.