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 one of the most common and irritatingly painful foot problems. It can strike at nearly any age, regardless of health status or activity level. There are a variety of possible causes of heel pain, but the most common cause are heel spur syndrome, or plantar fasciitis. To determine the cause of your heel pain, it's best have an evaluation by a podiatrist (foot specialist) or other health care provider.