It is widely thought that in the majority of domestic water systems in the UK, the immersion heater is only used as a backup for heating the potable (drinkable) water. These types of heaters warm the water with an electrical element or elements that screw into the cylinder. A West Heath Plumber can change defective heating elements. They are fitted to heat the cold water that is fed from the mains. These elements can succumb to something called scale. This scale will drastically reduce the efficiency of the element and affect the water heat. There is a routine to clean the deposits from the elements, but, if you are not confident to take this on, then, you need to call a professional plumbing service. Firstly you will need to isolate the power to the element(s) and drain the cylinder. Fit a rubber hose to the drain valve at the bottom of the water heater, and open the drain valve and a hot water tap. Once the cylinder is empty, undo and remove the access cover for the element with a screwdriver. There may be a need to move some insulation in order to see the element. West Heath Plumbers can work an all systems. Now, disconnect the cabling and remove the element(s) depending on how many are fitted. The element(s) is normally held by a series of bolts, or they have a threaded base that screws into the cylinder. Remove and clean the element, using a solution of sodium carbonate and water or vinegar mixed with water. (2 tablespoons of vinegar or 2 tablespoons of sodium carbonate in 1 quart of hot water) and a cleaning pad. Should the element be corroded you will need to fit a replacement. If your water is cooler than normal, erratic hot water, or a smaller than normal supply of hot water are all signs of an element that is damaged. Refit the cleaned or new element(s). Reconnect the wiring. Re-fill the cylinder by closing the drain valve and turning on the cold water supply valve.