Schematic of a sacrificial anode on a hot water tank (C) Carson Dunlop AssociatesHot Water Heater Anodes & Dip Tubes - Inspection, Diagnosis, & Repair
Water heater anode or water heater dip tube inspection & replacement.

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This article gives a definition of water heater anodes or dip tubes, explains what they are for, how they work, and what goes wrong with anodes and dip tubes.

A corroded or damaged dip tube or water heater anode can cause loss of hot water, water odors, and even debris showing up in the building water supply.

A bad water heater anode can produce a sulphur odor in hot water. A worn out water heater anode shortens water heater life. A leaky water heater dip tube can cause less hot water delivery to the home or debris in the water supply piping.

What is the difference between a water heater dip tube and the sacrificial anode? Are they the same part? How to inspect, diagnose, & replace water heater anodes and dip tubes.

The articles at this website will answer most questions about residential and light commercial water heaters as well as many other building plumbing system inspection or defect topics. Page top water heater drawing showing the sacrificial anode on a water heater is provided courtesy Carson Dunlop Associates, used with permission.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Check the Sacrificial Anode & Dip Tube of Your Water Heater Tank

Schematic of a sacrificial anode on a hot water tank (C) Carson Dunlop AssociatesReduced hot water pressure and flow and also sulphur smells or similar water odors in the hot water supply as well as debris in the water supply system might all be traced to problems with a water heater anode or dip tube.

Accumulated debris in a water heater, and debris from a corroded or disintegrating hot water tank dip tube or hot water tank sacrificial anode can also block the hot water outlet opening, resulting in low hot water pressure in a building.

Below we discuss the water heater anode and water heater dip tube in detail. This article describes the diagnosis and cure of debris in the building water supply traced to a deteriorated water heater dip tube/anode.

Functions of a Water Heater Tank Dip Tube:

The water heater tank dip tube, often made of a special metal to combine its function with that of a water heater tank sacrificial anode (to reduce water tank corrosion and leaks) performs these functions:

Functions of the Water Heater Anode

By inserting into the water heater tank a rod made of a metal which is more readily corroded than the steel of a steel hot water tank, the sacrificial anode protects the hot water tank from early failure due to corrosion. An illustration of the water heater anode is shown at the top of this page.

Low Hot Water Temperature Traced to Depleted Combination Dip-Tube & Sacrificial Anode

Schematic of a sacrificial anode on a hot water tank (C) Carson Dunlop Associates

At TEMPERATURE OF HOT WATER IS TOO LOW we explained that a leaky dip tube in a water tank can result in hot water temperatures that are too low.

But the dip tube on many water heaters also functions as a sacrificial anode, as we show here.

Here Carson Dunlop Associates' sketch shows the location of the sacrificial anode dip tube on an electric water heater.

Cold water is shown entering from a pipe behind the heater and entering at the bottom of the water tank.

But some water heaters use a "dip tube" that may also serve as the sacrificial anode.

Sulphur or Rotten Egg Smells in Hot Water Supply Traced to Water Heater Anode Problems

The role of the sacrificial anode is to protect a glass-lined steel water heater tank itself from corrosion - the water heater anode rod will gradually deteriorate or basically "dissolve" over the life of the water heater.

The rate of water heater anode depletion depends on the chemistry of the water supply (more aggressive water is more corrosive), and the amount of usage of the water heater - how much hot water is used in the building.

Watch out: if the water heater sacrificial anode rod completely dissolves or depletes, the water tank itself is no longer protected from corrosion and the tank may be damaged and its life significantly reduced.

If your hot water smells like rotten eggs, and especially if it's only the hot water, not also the cold water supply, you should definitely check the condition of the sacrificial anode on the hot water heater, no matter what kind of water tank you've got installed.

If the building water supply contains dissolved hydrogen sulfide gas (H2S), (also potentially explosive - see HYDROGEN SULFIDE GAS), then the combination of water chemistry and the presence of the sacrificial anode in the water heater tank can produce black debris in the water supply and an increased level of sulphur or rotten egg smells in the building hot water supply.

In fact if there is significant H2S in the water supply even the cold water may smell like rotten eggs. In our experience with private well water that contained H2S, the odor level varied by time of year, level of the water table in the ground, and usage of the well. Often returning from a month of vacation the homeowner would notice a stronger rotten egg smell in the building water supply.

If your water supply contains high levels of hydrogen sulfide, enough to smell, you should check with your plumber or your water heater manufacturer about purchasing and installing a special sacrificial anode that can reduce this smell problem in the building hot water system.

Additional water treatment to remove sulphur may also be needed.

Change to an aluminum anode in the water heater?

Aluminum anodes are used in water heaters to replace the standard magnesium anode where the local water supply is high in sulphur. That's to avoid a problem with the formation of hydrogen sulfide gas in the water heater - a rotten egg smell.

Watch out: if your water supply is both high in sulplhur and is alkaline, a reaction between alkaline water and an aluminum water heater anode can cause the formation of blue-green slime or gel deposits that can ultimately clog the hot water supply piping system.

If you experience that problem your water supply may need to be tested to confirm its alkalinity. You might need to install a treatment system to adjust the pH of your water supply.

Corrosive Water Supply Reduces Anode & Water Heater Tank Life

If your water supply happens to be highly conductive or corrosive (see WATER TESTING GUIDE) then the dip tub/sacrificial anode in the water tank may indeed corrode away until it leaks (dropping the hot water temperature) or disappears entirely.

Another cause of H2S odors in hot water may be traced to homes that use a water softener to treat their incoming water supply. Water that is high in salt ions (a water softener may replace calcium or magnesium with sodium or salt ions in the process of "softening" a hard water supply), can be extra corrosive in the water heater and can reduce the life of both the sacrificial anode and the water heater tank itself.

At ODORS in WATER we discuss the general problem of diagnosing and curing odors in water;

We provide a detailed list of sewer and sulphur gas odor sources at SOURCES OF SULPHUR ODORS IN BUILDINGS.

Also CHINESE DRYWALL HAZARDS discusses Chinese drywall odors, sulphur smells, and corrosive outgassing hazards in buildings. Major costs to remove this product, repair or replace electrical wiring, plumbing, and HVAC components may be involved, and there may be immediate safety hazards due to damaged smoke detectors or carbon monoxide detectors in buildings where Chinese drywall outgassing has caused damage.

Procedure to inspect a water heater Sacrificial Anode or Dip Tube

Water heater anode (C) Daniel Friedman

In our photo (left) our pencil is pointing to the water heater sacrificial anode fitting, viewed looking down on the top of the water heater. Often the word "anode" will be found embossed into the steel water heater top at this location.

In this case the sacrificial anode is a separate component that can be removed and replaced on the water heater tank.

The dip tube, not directly visible, is below that blue plastic ring that marks where cold water is entering the water heater tank.

Regardless of whether your water heater is electric, gas fired, oil-fired, or indirect fired from another heat source the sacrificial anode inspection and change out procedure is similar. We outline the procedure below.

For details also see DRAIN a WATER HEATER TANK

How Often Should the Water Heater Sacrificial Anode be Inspected?

Cleaning out a hot water tank (C) Daniel FriedmanWater heater installation guides we surveyed gave water heater anode rod inspection (and replacement if needed) intervals of 3 to 10 years, probably varying by water heater type and model and anode rod properties as well.

American Water Heater Co. recommends that the water heater sacrificial anode rod should be removed from the water heater tank every three years for inspection, and if the rod is more than 50% depleted it should be replaced.

If the water heater is installed in an area where the water is hard, or "aggressive" or "corrosive", inspect the water heater after 3 years, or for Rheem water heaters, every 5 to 8 years.

Rheem Corporation, a manufacturer of water heaters, recommends that the water heater anode be inspected after 8 years (Rheemglas™, RheemPlus™) to 10 (Rheem Optima) years depending on the water heater model.

Aluminum Water Heater Anodes & Alkaline or high pH water Causes Slime Formation

Inspect the water heater for deposits of a gelatinous Aluminum hydroxide (Al OH) slime at the heater drain, on the anode, and slime clogs at faucet strainers if you live in an area where water is acidic, and in particular if your water heater uses an aluminum anode. The result can be a rumbling or popping noise that may occur while the water heater is still rather new, with less than six months of service.

At RUMBLING WATER HEATER we explain that when the water supply has a high pH (pH of 8 or higher) and where the sacrificial anode in the water heater is made of aluminum. High pH means the water is too alkaline or too basic (not acidic enough).

The high pH water reacts chemically with aluminum to form aluminum hydroxide (Al OH) that appears as a blue, gray or green slimy substance collecting on the bottom of the water tank as well as on the surface of the sacrificial anode.

That slime can cause both rumbling noises in the water heater - similar to those caused by scale deposits, and clogging water faucets if the heater uses an aluminum anode.

The proper repair is to flush the water heater thoroughly and then to replace the aluminum anode with a magnesium sacrificial anode.

Is the Anode Aluminum or Magnesium?

On some water heaters such as those produced by A.O. Smith, you can identify an aluminum sacrificial anode by noticing that its capping plug surface is smooth. A magnesium anode plug or cap has a weld bead on the plug.

AOS Bulletin 14 ALUMINUM HYDROXIDE [PDF] for a description of cures for aluminum hydroxide slime clogging if no mineral scaling is also present, retrieved 2017/11/17 original source:

There the company notes:

Since aluminum hydroxide is a product of a chemical reaction dependent on the water condition, any treatment is not considered warranty related.

How to Replace the Water Heater Anode Rod - step by step

Water  heater anode location (C) D Friedman nee AWH On inspection, if your water heater sacrificial anode is corroded and pitted, or if the lower portion of it has dissolved completely, the anode needs to be replaced and you will need to shorten the interval at which you inspect this component.

It's a relatively small plumbing job to disconnect water pipes from the water heater and then pull and check, and replace the dip tube/sacrificial anode if necessary.

A great time to change the water heater dip tube or anode is when the water heater tank has been drained for some other reason, such as to de-scale or de-lime the water heater (as the worker is doing in our photo at left) -


Safety Warning: do not attempt to de-lime or de-scale an electric water heater without first making sure that the de-scaling chemical won't contact the sacrificial anode - otherwise an explosion or fire could occur.

The water heater anode location, for purposes of removal or replacement on most water heaters is accessed from the water heater tank. In our sketch of a water heater showing the anode location, the anode (red arrow) is inserted into the water heater tank top at the spot pointed to by the green arrow.

Usually this location is marked on the water heater top as "Anode".

Water heater drain valve (C) Daniel FriedmanHere are the detailed steps in replacing a water heater anode rod:

A higher hose destination will prevent the water heater tank from draining.

If your water heater drain valve happens to be high enough above the floor you can skip the hose hookup and just use a plastic pan or bucket as we show in our photo (below).

Water heater drain procedure using a plastic bucket (C) D Friedman R Arlyck

Some water heaters do not have a sacrificial anode rod. Instead these water heaters may use a chemically inert anode rod to which electrical power is provided to achieve the same anti-corrosion function.

Be sure to disconnect the anode rod electrical power before attempting water heater cleaning, and be sure to restore power after the tank is returned to operation.

Also see WATER HEATER FLUSH PROCEDURE where we describe the effects of a deteriorated plastic water heater dip tube.

How Long Should A Water Heater Last?

See AGE of WATER HEATERS for the answer as well as for our list of factors that affect water heater life.

Also see our list of types of water heater leaks at WATER HEATER LEAK REPAIR


Continue reading at WATER HEATER DEBRIS FLUSH or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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