A magnesium anode is a sacrificial rod fitted inside enamelled hot water tanks that corrodes deliberately so the steel tank does not. Together with the enamel coating it forms the corrosion protection system required by DIN 4753; the anode is a wear part that should be inspected roughly every two years and replaced when consumed.
Why enamelled tanks need an anode
Enamel (glass fused onto steel at ~850 °C) is an excellent barrier between water and tank wall, but no industrial enamelling is entirely free of microscopic pores. At those points, water would attack the steel. The magnesium anode fixes this electrochemically: magnesium is less noble than iron, so galvanic current flows from anode to any exposed steel, and the anode corrodes instead of the tank. DIN 4753-3 codifies this enamel-plus-cathodic-protection system for potable water heaters.
Inspection and replacement intervals
| Water hardness / conductivity | Recommended check |
|---|---|
| Soft, low-conductivity water | Every 2 years |
| Average municipal water | Every 2 years, replace at ~2/3 consumed |
| Hard or salty water, high draw-off | Annually |
An exhausted anode is the leading cause of premature enamelled-tank failure — a €30 part protecting a €1,000+ vessel. Warranty conditions of most enamelled-tank manufacturers require documented anode maintenance.
Magnesium vs powered (impressed-current) anodes
Electronic titanium anodes impose the protective current from a small power supply instead of consuming themselves. They never wear out and suit aggressive or very soft waters where magnesium dissolves quickly, at the price of needing a permanent 230 V connection. Magnesium remains the standard for most residential cylinders because it is simple, silent and grid-independent.
Anodes and tank types
Only enamelled steel tanks need sacrificial anodes. Stainless steel cylinders rely on their alloy's passive layer instead (with their own sensitivities, e.g. chloride content), and non-potable buffer tanks filled with closed-circuit heating water usually need no anode at all — one reason buffer and potable storage are engineered differently.
Frequently asked questions
What are the signs of a consumed anode?
There are no visible signs from outside — which is exactly why scheduled inspection matters. Indirect hints include rotten-egg smell in the hot water (anode-water chemistry) or rust traces at the drain.
Can I retrofit an electronic anode?
Usually yes, into the same threaded port, provided the tank is enamelled and the manufacturer approves. It removes the periodic replacement but adds a small standing electrical load.