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 a very common foot problem. The sufferer usually feels pain either under the heel (plantar fasciitis) or just behind it (Achilles tendinitis), where the Achilles tendon connects to the heel bone. Even though heel pain can be severe and sometimes disabling, it is rarely a health threat.