How to replace a magnesium anode in a water heater and why do it

The magnesium anode protects the water heater and heating elements from electrochemical corrosion. But over time, it collapses. If it is not replaced in a timely manner, this can lead to premature failure of the water heater. Have you heard of this for the first time? We will tell you everything in detail, and also show you how to properly replace the magnesium anode.

What is a magnesium anode and what is it for
The magnesium anode is a metal rod with a threaded tip. It is installed in the water heater tank , as a rule, next to the heating element.

It does not participate in the heating of water in any way and does not eliminate the formation of scale. The anode serves for galvanic cathodic protection of the tank against corrosion and rusting.

You can rightly notice that many modern water heaters use a stainless steel tank. But completely stainless steels do not exist. This becomes well understood if we proceed from the English name – Stainless steel, which literally translates – less rusting steel. This type of steel resists corrosion due to the thin protective film on its surface. But under the influence of an unfavorable environment that arises inside the water heater, it can collapse.

The enamelled coating of tanks is also subject to degradation due to constant heating and cooling cycles. After all, paint and steel have different coefficients of thermal expansion. First, small cracks appear, which increase in size over time.

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Water heater Ariston VELIS TECH INOX PW ABSE 80 21 999 *
In short, corrosion is an electrochemical redox reaction. Two processes occur simultaneously: oxidation, when electrons are transferred from the surface of iron (leading to its actual loss), and reduction, when electrons convert water or oxygen to hydroxides.

But, if a protective anode is present in the water, magnesium takes over all oxidative reactions, since it has the lowest electrochemical potential. All destructive processes are directed precisely at him, and not at the walls and welded seams of the tank. And the scale becomes loose as a result of the reaction. When cleaned, it can be easily removed.

The magnesium anode protects the storage tank from corrosion and increases its service life.

The length, diameter, size of the threaded connection of magnesium anodes are different. It depends on the manufacturer and the volume of the water heater. But even if you cannot find the original anode on sale, you can always choose a compatible one.

Why change the anode
Magnesium effectively stops corrosion of the tank walls and welds. But over time, the anode oxidizes and gradually collapses. The protective function decreases, and then stops altogether – the tank can rust through:

In addition, due to the mineral salts dissolved in the water on the inner surface of the tank , scale forms water heater and on the surfaces of heating elements. Without a magnesium anode, these deposits become incredibly strong and dense. As a result, the correct heat exchange is disrupted, which can lead to burnout of heating elements .

Magnesium anodes are consumables. Manufacturers recommend checking their condition annually. Depending on the hardness of the water, replacement is carried out at least once every 24 months, and also if the anode is worn out by 30% or more.

Required tools

You don’t need a lot of tools to replace the magnesium anode. Prepare:

New magnesium anodes to match your water heater .
Draining water and removing heating elements
Replacement of magnesium anodes will be demonstrated on the example of the Ariston ABS VLS EVO INNOX QH 80 water heater .

Be sure to disconnect the water heater from the power supply and turn off the water.

Be careful. The water in the water heater is very hot! Before starting work, it is better to completely drain it or turn off the heating in advance.

Release excess pressure from the boiler by opening a hot water tap. Then close it. Disconnect the drain hose. Unscrew the flexible hose and the non-return safety valve from the cold water inlet. Use an adjustable wrench if necessary. Prepare a napkin as some water may leak out.

Connect the prepared flexible hose to the water heater inlet.

Direct its other end to the place where you plan to drain the water. If the toilet, sink or bathtub is far from the place where the water heater is installed, then you can use, for example, a bucket.

Carefully loosen the hot water connection. Do not unscrew it completely. In case you need to stop the water, just tighten the nut again.

The water from the water heater will start to drain.

Then remove the decorative plugs and unscrew the screws with a screwdriver.

Remove the cover of the water heater, under which there are heating elements and the magnesium anode itself.

At this stage, it is recommended to take several photos of the wire connections and a general view of the connection diagram. When reassembling it will help a lot, and you will not confuse anything.

Disconnect interfering wires.

Place a container into which the remaining water in the tanks will be drained. There won’t be much of it, but it will be very dirty.

Unscrew the heating element mount . This can be done with a key, but in this model, due to the limited space, it is convenient to use a socket head .

Be careful, water may come out suddenly when you don’t expect it.

Water heater Gorenje OGBS80SMSB6

Remove the heating element. The sight is unpleasant, but the visible dirt is for the most part just the remnants of the magnesium anode. In this case, in two years, it almost completely collapsed. There are also deposits inside the tank – remove them with a disposable cloth.Replacing the magnesium anode
Magnesium fell off the anode and can no longer perform the function of protecting the tank, so the anode must be replaced.

The heating element must be rinsed with water, and the remains of the anode must be unscrewed. Be careful, its edges are very sharp! Use pliers to avoid injury . Screw in the new anode without using a tool.

If the water heater has two heating elements and, accordingly, two magnesium anodes, follow the same steps. In this case, the condition of the second anode is also unsatisfactory:

For comparison – new and old magnesium anodes.

Assembly is carried out upside-down. Clean the edges of the heating element holes well. Install the retaining screws in the mounting locations.

Put the sealing gasket on the heating element and carefully install it in place. Tighten the nuts evenly crosswise to avoid skewing. Make sure that the contacts of the heating element are dry and reconnect all the wires, referring to the photo.

Using an anaerobic sealant or fumant, install a safety check valve with a drain hose and connect water to the water heater. Remember to tighten the nut on the hot water outlet .