Problems with water temperature are often an indication of a faulty immersion heater
Faults to immersion heaters are often caused by hard water (lime scale) build up within the tank. This eats away at the copper element and causes it to short circuit or sometimes just not heat up. The element is encased inside the tank of water and requires a skilled, experienced workman to replace it. The water has to be drained away before the element can be removed. Great care has to be taken not to cause any leaks or air locks on refilling the tank.
Other faults include the power failure to the switch or element which can be carried out on our hourly rate.