Every brand of mains pressure hot water storage heater with a vitreous enamel (glass) lined tank is fitted with one or two sacrificial anodes. This ensures that corrosion can’t take place during the warranty period of the tank. It is no coincidence that most manufacturers warranty period is 5 years which is generally the life span of an anode. Note, in certain areas with hard water an anodes life span can be as little as 24 months.