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: There are many possible causes of heel pain. A common cause of pain on the bottom of the heel is plantar fasciitis. Pain to the back of the heel may be caused by Achilles tendinitis.