Heaters are, of course, hot! The very high heat on the skin of the heater causes dissolved minerals like calcium to precipitate out of solution. The precipitant attaches itself to those hot spots, insulating the skin from the cooling water. Heat that can’t get out builds up inside and, if it gets hot enough, heater failure will occur. Always keep the heater’s skin as cool as possible by making sure it has a rapid flow of
water over its hot zone. Never let the water get too low.

Heater life can be greatly extended by removing insulating deposits as soon as possible. In hard water, inspect heaters for deposits as often as once weekly during usage. You will notice discoloring of the metal and/or rough surfaces on the heater element. It doesn’t take very much to cause a serious problem. After inspecting every week, you will soon learn how frequently the water conditions warrant heater cleaning.

To clean the heater, unplug the power and allow heater element to cool. Remove heater from the water and treat with a diluted bath of nitric acid (rust remover) or citric acid. Be sure to wear eye protection and rubber gloves when working with acid. The heater should only require this bath for several minutes. When the scale deposits begin breaking up or dissolving, remove the heater from the acid and wipe down with a cloth until deposits are gone. Rinse with water to prevent acid from affecting the system. Place heater back into service. If an acid solution is not handy, use a steel wire brush to brush off the deposits.