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.....
Another common cause of heel and calf pain is Achilles Tendinitis. Symptoms are frequently described as an aching pain in the back of the lower leg and just above the heel. This sensation is typically worse after exercise and upon first waking up in the morning.
Heel pain is a common symptom that has many possible causes. Although heel pain sometimes is caused by a systemic (body-wide) illness, such as rheumatoid arthritis or gout, it usually is a local condition that affects only the foot. The most common local causes of heel pain include: