Problems With the Magnesium Rod in the Water Heater

Written by john brennan
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Problems With the Magnesium Rod in the Water Heater
Some hot-water heaters are equipped with magnesium anodes. (plumbing image by Inger Anne Hulbækdal from

Many hot water heaters are equipped with magnesium anode rods to reduce corrosion; the magnesium corrodes in place of the steel and thereby helps to protect the tank. Under certain circumstances, however, magnesium anode rods can cause other problems.

Time Frame

Magnesium anodes have a limited lifespan; since they are intended to corrode over time, they will periodically wear away completely, at which point corrosion of the steel tank will accelerate if the rod is not replaced. A 1997 Popular Mechanics article on hot water heaters recommends you check your anode rode annually.


If your water contains sulphates, magnesium anode rods also can react with the sulphates to produce trace quantities of hydrogen sulphide, lending a peculiarly unpleasant rotting egg scent and flavour to your water. The key sign is that the rotting egg odour is only associated with hot water, not with cold. Hydrogen sulphide also can be caused by bacteria colonising your water heater.


Magnesium anode rods serve an important function in your hot water heater, so you don't want to remove them needlessly. If you find your hot water has a hydrogen sulphide smell/taste, consult with a water heater dealer to determine whether the magnesium anode or bacteria are more likely to be the cause. If the magnesium anode rod is indeed the problem, you can often replace it with a rod made of a different material like aluminium and thereby solve the problem.

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