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.
Plantar fasciitis: Most common cause for heel and foot pain is plantar fasciitis which is an inflammed fascia or ligament that supports your arch. It originates in the heel and ends in the toes. When you pronate or your arch flattens than there is tension in this band of tissue causing pain and inflammation.