Heater Service Life - Tech Talk 55
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 heater casing from the cooling water. Heat that can't get out builds up inside and, if it gets hot enough, heater failure will occur. Always make sure the heater has a rapid flow of water over its hot zone. Never let the water get too low or let a crust build up on the casing.
Heater life can be greatly extended by removing insulating deposits as soon as possible. In hard water, inspect heaters for deposits once weekly initially and then as experience dictates. It doesn't take very much to cause a serious problem.
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), citric acid or other lime and scale deposit remover. 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. Rinse with water. Place heater back into service. If an acid solution is not handy, use a steel wire brush to brush off the deposits. Be sure to clean the area where the small diameter tube rests behind the heater tube, as this area is especially vulnerable to deposit buildups. Care should be taken not to scratch, gouge or wear away the metal surface of the heater when using the brushing technique.