Gazing at an Anode Rod

Most people in the U.S. have tank-type water heaters, and most of these tanks are glass-lined.  Yet almost nobody looks at the anode rod, which is the biggest key to making your water heater last a very, very long time.  So here I’d like to talk about how to look at an anode rod and why you might want to gaze intently at it sometimes.  If you do, ultimately you can be rewarded by having your water heater last fifty or more years!

Designed to fail

The anode, properly known as the sacrificial anode rod, is installed in all glass-lined tanks specifically so that it will corrode away.  What?!  Why put in a part just so it will fail?  To protect the steel tank.

We all know that if you get steel wet, it rusts.  Rusting is a chemical reaction that occurs when oxygen turns steel back into iron ore.  Because fresh water always has some air in it (and air is about 21% oxygen), wherever water touches the steel tank, rust can happen.  [The water heater tank below has a lot of corrosion.  The diagonal piece is the remainder of the bottom half of the anode rod.]

This is why steel water heater tanks are lined with glass; a glass coating has been baked on, like the enamel on your coffee mug.  This forms a barrier to keep oxygen from getting to the steel.  There are always little imperfections in that coating, where the coating took a holiday from doing its job and left the steel exposed to water.  This is where rust can and will happen.  Surprisingly, these imperfections are called “holidays”!

Your water heater is a battery

If we throw in another metal—magnesium or aluminum—along with the water, now it becomes an electrochemical reaction.  A measurable direct current is generated, just like what happens with batteries.  In batteries, we often use that current so that we can see in the dark (as in a flashlight).

But another thing is happening when that current is formed:  One metal is sacrificing itself, and the other metal is suffering no measurable damage.  In other words, with a water heater, the rusting of steel in the tank is prevented by having that anode corrode away instead.  (By the way, about 0.8 volt is generated between magnesium and steel, so if you really wanted to you could hook two water heaters together to make a flashlight—but it might be a bit cumbersome.)

The speed of failure

Water is the electrolyte, or the thing that lets current flow from the positive anode to the negative tank (cathode).  The more mineral dissolved in the water, the more conductive it is and the faster the anode gets used up.  You expect anodes to last at least five years in nice water.

But I’ve seen them completely used up in as little as six months in over-softened water.  All of the hardness (calcium and magnesium) in the water has been removed and replaced with salt, which is more conductive.  With this water, the anode works too well in protecting the tank!  It works so well that excess hydrogen gas is formed, causing spurting at the taps and often a rotten egg odor.  You don’t want overly conductive (overly softened) water.

Removing the anode

All this leads up to actually looking at the anode, because it will tell you a whole lot about what’s happening inside your water heater, if you know how to look.  Most people don’t look at anodes because they don’t know about them.  Also, it can be difficult to get to them out.  Because checking and replacing anodes isn’t common practice, most plumbers don’t have the right tools.  Most manufacturers do say in their literature that the anode should be checked, but not everybody takes the time to read instructions.

To look at your water heater’s anode, follow these steps:

• Have the right tools, and a replacement anode on hand.
• Turn off water and power to the heater, and have no pressure at all in the tank.  [See this short video clip for what can happen if there is pressure.] 
• Locate and unscrew the rod.
• Anodes come in two types: hex-head or combo rod (which is part of the hot-water outlet).
• If you have a combo rod, all you’ll need is a 14” or larger pipe wrench.
• If you have a hex-head anode, you’ll want a 1-1/16” socket with at least a ½” drive (3/4” drive is better).  It’s best if the socket is a six-point type; its six internal sides fit the anode better than the normal 12-point type.
• You’ll want a long breaker bar and probably a “cheater” pipe to increase length and leverage.  I’ve used a small sledgehammer on the breaker bar, while pushing on the bar pretty hard to break the anode loose.  It’s the human impact-wrench trick!

Inspecting the anode

Let’s hope you’ve been successful and are now gazing at the anode itself, still warm from the hot water in the tank.  Look at how the anode in the tank compares to the new one you got.  (Note that, even if your anode doesn’t need to be replaced yet, it’s good to have a new one on hand before removing the old one; if you don’t need to replace the anode now, you’ll want to later.)

The photo above shows both new and used anodes.  That big fat one toward the center is a commercial magnesium rod.  Note the grey color.  Just above it is an aluminum anode.  See how much brighter the color is?  A better photo of just those two is below.  (Note: I’m not a fan of using aluminum in any water that might be used for cooking, bathing, or drinking, as there are health concerns.)

The right time to replace the anode

Now, have a look at a partially eroded anode rod (below).  It’s a magnesium rod that is ready for replacement.  Notice the fairly even corrosion on it?  Notice the bare wire on both ends?  When a rod has about six inches of bare steel-core wire, that’s the right time to replace it.  It’s served its useful life and hasn’t let rust start chewing on the steel tank.  If too much core wire is showing, the protection has diminished.

When you do check the anode rod and find that you need to replace it, you may find that the water heater is in a room that’s not tall enough to insert a full-length rod.  In that case, you can use a segmented anode rod.  The lead photo above shows what it looks like.  Because you have flexibility between each two segments, you can get the whole length into the tank.

Passivation, aluminum, and the powered anode rod

Sometimes the rod looks like that ones below; both are pretty much intact but coated over with a hard calcium carbonate layer.  As a result, they weren’t doing their job.  For its age, there should have been less metal remaining.  This is called “passivation.”  It’s not your friend.  It can happen in really good, clean, poorly conducting water.

Then there is the used aluminum anode.  See how it’s split?  Aluminum rods corrode in this interesting way, where chunks of the metal just fall off the rod—to the bottom of the tank, where they do no good.  As the aluminum in the tank corrodes, it produces volumes of a bluish, gelatinous goo.

This can encourage a gas water heater to make boiling, thumping noises, and the water is absolutely something you don’t want to ingest.  If you have an aluminum anode rod in your water heater and a recirculation line tied into the drain of the water heater, it could put this stuff into your water if the check valve doesn’t work.

What isn’t in the picture above is a powered anode rod.  It operates differently than a sacrificial rod.  A powered anode is plugged into the wall for its driving energy.  It has no corrosion byproduct, and is great for fighting that rotten-egg odor.  The only thing you need to look at with a powered anode rod is the indicator light to make sure it’s still doing its job.

Don’t forget to gaze

There’s a lot more to learn about anodes, but now you have the basics of how to “read” one.  This knowledge can help you to never need to get a replacement water heater on a holiday when you have guests!  Water heaters know how to get even if you don’t pay them enough attention.  So look fondly upon them and gaze at their anodes.  You’ll be rewarded.

 

This is a guest post by Larry Weingarten, a self-described hot water nerd who lives on the Monterey peninsula in California.  Larry is my go-to guy when I have questions about plumbing and hot water.  This article is from his upcoming book, The Philosopher’s Toolkit, which will be a followup to his last book, The Philosopher’s Wrench.*

 

* This is an Amazon Associate link. You pay the same price you would pay normally, but Energy Vanguard may make a small commission if you buy after using the link.

 

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