Choosing an anode means choosing a maintenance regime, not a lifespan. A magnesium anode is a consumable that dissolves in place of the steel, a titanium anode is never consumed but protects nothing without the electronics driving it, and impressed current only works for as long as it stays energised. France's Agence Qualité Construction, in its building pathology sheet on corrosion of steel domestic water circuits, sets out the parameter no anode will ever compensate for: never exceed 60°C, hold to 53°C during the first months in service, and never drop below 50°C at any point of the distribution network.
Understanding why your hot water tank corrodes and how the anode protects it
Internal tank corrosion: what's really happening inside the cylinder
As water heats up, it carries in oxygen and mineral salts. A tank's steel cylinder is protected by a lining, but at the smallest micro-defect, the steel is exposed again. The result: an electrochemical reaction starts, just like a battery. Corrosion first attacks the vulnerable spots (welds, fittings, the bottom of the tank), then eventually perforates it. The AQC separates four mechanisms, and the anode only addresses part of them.
| Mechanism identified by the AQC | What triggers it | What you find |
|---|---|---|
| Dissolved-oxygen corrosion | aerated water in contact with steel | pitting of varying depth, ferrous hydroxide deposit, internal pustules |
| Galvanic couple | dissimilar metals in contact, copper upstream of galvanised steel, a case explicitly prohibited | preferential attack on the less noble metal |
| Differential aeration | uneven oxygenation across the same metal | anodic and cathodic zones, localised corrosion |
| Microbial growth | prolonged stagnation of the water | sulphate-reducing bacteria, significant corrosion |
Sacrificial protection or electrical action: the two main anode families
A "sacrificial" anode (usually magnesium) dissolves in place of the tank. It's simple and effective, but it wears out. The other family, the impressed-current anode, maintains protection through a small electrical power supply. It wears out less, but must stay powered and monitored.
Warning signs of insufficient protection: water, noise, sludge and leaks
On site, watch for discoloured hot water, crackling noises, sludge when drawing water, or seepage at the base of the tank and at the relief valve. When these signs appear, the anode is often worn out or poorly connected. A check-up prevents a surprise leak.
Magnesium anode: the classic solution for protecting a tank, and its limits
How the sacrificial anode works: magnesium is "consumed" in place of the tank
In a hot water tank, the magnesium anode acts as an anti-corrosion fuse. Magnesium is more "reactive" than steel. It dissolves first when water attacks vulnerable spots (micro-cracks in the enamel, pitting). As a result, the tank stays protected as long as the anode still has material left.
When it holds up well: water hardness, temperature, usage and tank volume
It holds up well with fairly hard but not extreme water, a temperature set around 55 to 60°C, and regular use that renews the water. Its limits show up when the water is very aggressive (low-mineral, softened, or with certain treatments), when the temperature is high, or on a large, heavily used volume. In these cases, the anode can wear out fast, and protection drops with no visible sign.
Maintenance to plan: check frequency and replacement to prevent corrosion
To avoid a tank perforating "without warning," plan a regular check of the anode, often every 1 to 2 years depending on water quality and temperature. Replace it as soon as it's heavily worn (or too thin). While you're at it, descaling and checking the safety valve also extend the tank's life.
Titanium anode and impressed-current anode: enhanced protection for certain tanks
Titanium anode: an anode that isn't consumed, but needs a matching system
In some hot water tanks, the titanium anode is called non-consumable because it doesn't dissolve the way a magnesium anode does. It acts as the support for active protection. Without an electronic control box and power supply, it doesn't do its job. As a result, the tank can stay protected longer, especially in so-called aggressive water.
Impressed current: how anti-corrosion protection is controlled and what changes on site
The principle is simple. A control board sends a weak direct current to the titanium anode to polarise the tank and limit corrosion. The system adjusts protection based on the tank's condition and the water. On site, plan for running the cable, the electrical connection, and a visual check of the indicator light or diagnostic once the tank is filled.
Points to watch: power supply, control board, faults and compatibility by tank model
- Don't cut the power for extended periods. Without current, protection stops.
- Check that the control board is present, accessible, and protected against moisture.
- In case of a fault, follow the manufacturer's error code. Replace with an identical part, especially on enamelled tanks.
Choosing the right anode based on the tank, the water and the installation context in 2026
A simple decision matrix: tank type, water quality, maintenance frequency and client budget
Start from the tank (enamelled steel or stainless steel), then look at the water and how much maintenance capacity there is. In practice, you're choosing between a magnesium anode (simple, needs replacing) and controlled-anode systems (ACI-type), which cost more but are steadier. The three families are not separated by a claimed lifespan, but by what they demand of you after the install.
| Protection | Principle | Consumable | Electrical supply | What you check |
|---|---|---|---|---|
| Magnesium anode | sacrificial anode, dissolves in place of the steel | yes | none | remaining section, exposed core, replace at the visit |
| Titanium anode, ACI type | inert support for active protection | no | yes, via the tank's electronics | signal present, manufacturer diagnostic |
| Impressed current | direct current applied to polarise the cylinder | no | yes, at all times | voltage present, continuity, fault code |
- Enamelled steel + easy maintenance. Magnesium, periodic check.
- Enamelled steel + infrequent maintenance. ACI, if the power supply is reliable.
- Stainless steel. Check the manufacturer's recommendation, sometimes no anode is needed.
Practical cases: tank in a hard-water area, aggressive water, second home, large hot water volume
Hard-water area. Limescale insulates the heating element, so think about scaling too, not just corrosion. Aggressive water (very soft, conductive). Favour active protection and keep an eye on the setting. Second home. Avoid solutions that dislike power cuts, or secure the power supply. Large hot water volume. Fewer shutdowns, planned maintenance.
In 2026, how to secure the tank's lifespan: warranty, parts availability and total cost
Check the tank warranty and its maintenance conditions. Ask about the availability of parts (anode, ACI board, seals) and their price. In the end, compare the total cost over 10 years, not just the purchase price. The exact reference of the cylinder and of its protection is locked down at pricing stage: Argile keeps a catalogue where the fitted reference, its technical data and its price are verified.
Installation and maintenance best practices to limit tank corrosion
Useful settings: hot water temperature, anti-legionella and impact on corrosion
The setpoint sits between two documented limits: never above 60°C according to the AQC, and never below 50°C at any point of the distribution under the amended French order of 23 June 1978. On commissioning, the AQC also asks you to hold to 53°C for the first months, while the lining stabilises. Above 400 litres of storage, the water has to be at 55°C or more at the outlet at all times, or undergo a daily temperature rise: that is the anti-legionella regime taking over. Keeping it too hot continuously speeds up scaling and can encourage internal corrosion. The downstream thermostatic mixing valve is what lets you hold a high setpoint without breaching the draw-off caps.
Checks to schedule: anode inspection, measurement, descaling and seals
Schedule a regular anode check, especially with hard water. Replace a magnesium anode once it's well worn. On an impressed-current anode, check the indicator light and electrical continuity. Descale if heating time gets longer or the tank "clunks." Use the visit to check the seals, flange and safety valve too.
What you put on the quote and what you record for the warranty
The quote has to name the protection fitted, its manufacturer reference and the maintenance regime it imposes, because that document is what separates you from a cheaper bid that priced a magnesium anode where the tank expects an ACI control box. On an impressed-current install, state explicitly that the supply must stay energised, otherwise the protection drops out and the cylinder warranty with it. Record at every visit the setpoint measured, the state of the anode and the date, with a photograph: that is the only usable evidence in a dispute over a perforated cylinder. A documented follow-up is also what protects your liability cover.
