Hot Water Anode Replacement: What It Does and When to Change It

A sacrificial anode is a consumable rod fitted into a hot water storage tank. It is designed to wear away so that the cylinder around it is protected. Rheem's owner's guide for its electric storage heaters puts it plainly: the anode slowly dissipates while it protects the cylinder, and the life of the cylinder may be extended by replacing it.

That is the whole idea of anode replacement: the anode is the part designed to wear out, so the cylinder does not have to. Once the cylinder itself leaks, though, no anode will save it. A leaking cylinder is not repairable, which is why the anode is worth thinking about while the tank is still sound.

Rheem's electric guide describes its cylinder as vitreous enamel (glass) lined steel, protected by an anode. The tank does not have to be electric. Rheem's Australian owner's guide for its 551 series heat pump water heater carries the same anode section, lists anode inspection in its five-year major service, and gives the same reason: the anode dissipates while it protects the cylinder.

Not every water heater has one, and cylinder designs differ between brands and models. A continuous flow unit stores no water, so the question does not arise there. For a tank, the reliable answer is the owner's guide for your exact model, found from the model number on the rating plate. If the guide has an anode inspection section, your tank has an anode, and that section is where the schedule for your system lives.

Water chemistry is the main driver of anode wear. Manufacturers measure it as total dissolved solids (TDS), the amount of material dissolved in the water. Rheem chooses between green, black and blue anodes according to the TDS of the supply, with black typically fitted as standard.

The supply itself matters too. Rheem's electric guide singles out softened or desalinated water, a supply that alternates between a water tank and town water, and variable supplies such as bore water, and asks for more frequent inspection on all of them. More broadly, Rheem lists water chemistry, water pressure, inlet and outlet temperature, and usage pattern as factors in how long a water heater lasts. Two identical tanks on different water can need very different anode attention.

There is no universal anode replacement interval, because each manufacturer sets its own for each model and water type. Rheem's electric storage guide is a useful example of how specific that gets. It recommends a major service every five years that includes inspecting the anode and replacing it if needed. Where the water is softened, desalinated, switches between tank and mains, or comes from a variable source, it asks for the anode to be inspected within five years of installation and every three years after that. For any water supply, it puts the latest point for replacement at ten years after installation if the anode was not changed at a major service.

Those figures belong to one manufacturer's product, and even the same manufacturer varies them. Rheem's guide for its 551 series heat pump sets the latest replacement point at eight years after installation rather than ten. Another brand, another model or another water source can carry different numbers again. The QBCC's home owner's guide makes the same point from the regulator's side: follow the manufacturer's servicing recommendations, and a system on bore water or rainwater may need servicing more often.

A depleted anode rarely announces itself from outside the tank. The rod sits inside the cylinder, and Rheem's guides do not schedule anode work around a symptom list; they schedule an inspection by a qualified person, with replacement if the anode shows any sign of depletion. That is why the major service is framed as inspect and, if required, replace.

What you can see from outside are warning signs of a different kind, such as rust staining on the casing. That is worth a call rather than a wait for the next service, because if the cylinder itself is leaking the conversation is about replacement, not an anode.

Anode replacement is not a DIY job. Rheem's guide states that changing an anode must be carried out by a qualified person, and that servicing a water heater must only be done by qualified personnel. Fitting the wrong one has consequences too: Rheem warns that an incorrect anode can become overactive, letting hydrogen gas build up at the top of the heater during long periods of no use.

The regulator's view points the same way. The QBCC says most plumbing work in Queensland is regulated and needs a QBCC licensed plumber, and its list of unregulated jobs an owner can do covers things like shower heads and tap washers, not the internals of a hot water cylinder. If your tank needs an anode check, talk to a licensed plumber.

An anode can affect the cylinder warranty in two ways, so the booklet is worth reading before deciding to skip a check. First, the anode has to suit the water. Rheem covers its vitreous enamel cylinder only when the water's TDS is under 2500 mg/L and the correct colour coded anode is fitted, and faults caused by an incorrect anode are excluded.

Second, the anode itself is not a warranty item. Rheem's guide states that routine replacement of components such as the anode and relief valve is not covered by its warranty and is charged for. Rheem's current warranty terms also let it reject a claim if no major service was arranged in the fifth year after installation and that service would have detected and fixed the fault. Other manufacturers set their own terms, so the owner's guide for your model is the document that governs. Keep any service paperwork with it.

A new anode is worth fitting when the cylinder is still sound and the rest of the system is in reasonable shape. It is not worth fitting when the cylinder is already leaking, because the anode protects against corrosion and cannot repair it. It is also hard to justify on a tank that is near the end of its expected life for other reasons, where the money is better put towards the replacement that is coming anyway.

Access can decide it too. Rheem's installation advice is to leave headroom of one water heater height so the anode can be inspected or replaced, and it warns that the entire water heater may have to come out later for servicing. A tank squeezed under eaves or into a cupboard may need extra work just to reach the anode, and a plumber should say so before starting.

Start with the paperwork, not the tank. Find the model number and installation date on the rating plate, then find the owner's guide for that model and read its anode and maintenance sections. Note where your water comes from: town water, a rainwater tank, a bore, or a mix.

For town water, Unitywater describes Sunshine Coast and Noosa drinking water as generally soft, and Moreton Bay drinking water as neither hard nor soft. Unitywater also notes that soft water may be more corrosive to pipes, depending on pH, alkalinity and dissolved oxygen. Hardness is not the same measure as the TDS figure manufacturers use for anode selection, so treat it as a reason to check, not an answer. Its postcode checker gives the water quality details for your area. Properties on rainwater or bore water fall into the supply types manufacturers flag for closer attention.

RCM's servicing visit includes the anode where it is accessible and the tank's age warrants it.