This simple water heater check can prevent unexpected leaks and water damage

It takes only a few minutes but most homeowners don’t know to do it. A brief inspection of your water heater pipes can reveal an obvious trouble-sign and possibly a significant problem. A quick look will show if there is corrosion on the pipes connected to the top of your water heater.

A common situation

Many water heaters develop leaks at the pipe connections on top. Manufacturers usually provide two special steel pipe fittings that are threaded into the top of the steel tank. It’s typical for steel water heater tanks to have the cold water inlet pipe and the hot water outlet pipe connected to these fittings using copper fittings and pipes.

40 gallon water heater
A typical 40-gallon water heater showing the threaded copper to steel tank connections.

When copper and steel are connected together in the presence of a conductive liquid (the water in the pipe), an electrochemical reaction occurs that causes the steel to corrode at the point of connection. This process is called galvanic corrosion. It’s the same thing that occurs in a simple battery. The degree and speed at which this process happens will vary based on the quality of your water.

galvanic corrosion steel pipe
Damage to steel pipe threads from copper-to-steel galvanic corrosion. The full depth of the threaded pipe connection was dissolved away by galvanic corrosion. Compare these corroded threads to new threads shown in the inset photo.

The special galvanized steel fittings installed by the manufacturer are called dielectric fittings. They have a plastic tube within the steel pipe that is intended to internally seal on both ends and prevent the steel pipe from contacting the water within the pipe. If the steel is not in contact with water, corrosion can’t occur, even though the copper and steel are directly connected.

dielectric fitting
A dielectric fitting is made of steel. It has an internal plastic tube with extended sealing rings on each end. When properly installed, the steel does not make contact with the electrically conductive water in the pipe.

For a variety of reasons, these fittings can develop imperfect internal seals at the threaded ends. Once water leaks past the seal and makes contact with the steel and copper connections, corrosion begins. Galvanic corrosion will dissolve the steel pipe threads within the copper fitting connected to it.

Here’s what to check

A simple visual check of the pipes and fitting at the top of your water heater should reveal any signs of corrosion. If you can see corrosion at the connection between the steel and copper fittings, this could be an indication that galvanic corrosion is occurring.

corrosion copper steel joint
A copper water pipe connected to the steel water heater dielectric fitting. Corrosion is visible at the threaded pipe joint. This warrants calling a plumber for further evaluation.

The corrosion process dissolves the steel pipe threads and severely weakens the pipe joint. It’s more serious than a simple pipe thread leak. Excessive water pressure from fast-closing automatic water valves used on washing machines and dishwashers can cause a weakened pipe-joint to burst unexpectedly.

No corrosion at copper to steel joint
A copper to steel connection showing no signs of corrosion at the threaded joint. This photo passes the visual inspection.

If you find corrosion on copper-to-steel joints, it’s time to call your licensed plumbing contractor for a closer look. Your plumber can verify that the installation meets all of the local code requirements to prevent or reduce galvanic corrosion.

If corrosion has occurred at the pipe joints, new pipes and fittings will be required at the damaged locations. It’s best to catch and correct this early before it advances to a sudden and unexpected pipe burst and severe water damage to your property.

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© 2018 The Hartford Steam Boiler Inspection and Insurance Company. All rights reserved. This article is intended for information purposes only. All recommendations are general guidelines and are not intended to be exhaustive or complete, nor are they designed to replace information or instructions from the manufacturer of your equipment. Contact your equipment service representative or manufacturer with specific questions.

John A. Weber

John Weber is principal electrical engineer for HSB. He has over 25 years’ experience in solving facilities and electrical engineering challenges.


  • can you send this to me via e-mail? I tried printing the article but it won’t print and I want to share it with a handfull of my clients.

    835 N. STERLING AVE SUITE #230
    PALATINE, IL 60067-2284
    PHONE #847-963-8532

  • Use brass fittings with flexible connectors.That way there is no corrosion and in event of earthquake the connectors will flex,instead of breaking.

  • I would also like to have the article sent to me in a pdf…its a great article to share with our commercial and personal clients.

    Thank you, Gwen Crowell
    W M Jones & Co.

  • Per some of the other readers, can you send me the pdf to share?

  • Very good information for the homeowner. Generally speaking a residential water heaters life span is 10 to 12 years depending on use, temperature of the water being heated, water condition, high or low PH. Something I have often instructed my customers to do is a once yearly blow down, or drain down of their water heater. This can be a little risky depending on the drain valve at the bottom of the water heater, plastic -vs- brass. Plastic has a tendency of plugging up and not closing securely. If you do drain down the water heater and feel comfortable doing so, it will flush any of the hard water scale and mineral debris that build up in the bottom of the tank. While performing this task of drain down, try the pressure relief valve as well. Make sure it seats properly. If in doubt call a licensed plumber. A service call is much less expensive than a water heater leak and replacement. Generally at the least convenient time.

  • I didn’t know that steel pipe threads could corrode and weaken the pipe joint. My wife and I need someone to repair our water heater soon. We’ll make sure to find a professional that can get the job done right.

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