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.
Again, plantar fasciitis is usually brought on by a biomechanical imbalance of the foot, which causes inflammation of the soft tissues of the feet. If you are inactive most of the time, but suddenly find yourself on your feet for days at a time, you may see an increase in heel pain.