Dielectric Unions in Laguna Niguel Homes: Why Copper Meets Steel at the Water Heater and How Galvanic Corrosion Starts
Crusty, leaking fittings on top of a water heater are often galvanic corrosion where copper meets steel. What a dielectric union or nipple does, where else dissimilar…
Open the water heater closet or garage in many Laguna Niguel homes and you will find the same scene: white and green crust on the fittings at the top of the tank, a rusty stain down the side, and connectors that look older than the heater. A lot of that damage comes from galvanic corrosion, and the part designed to prevent it is called a dielectric union.
What galvanic corrosion is
When two different metals touch in the presence of water, they act a little like a battery. A small electrical current flows from one metal to the other, and the less noble metal slowly corrodes. In home plumbing the classic pair is copper and steel. Copper supply lines connect to the steel nipples on a water heater, or to an old galvanized line, and the steel side wears away from the inside, often at the threads.
What a dielectric union does
A dielectric union separates the two metals with a plastic or rubber insulator, so they are mechanically joined but electrically isolated. Dielectric nipples, which have a plastic lining, do the same job and are common on newer water heaters. The plumbing code calls for a way to keep dissimilar metals apart at joints like these, and inspectors look for it.
The catch is that dielectric unions are not forever. The gaskets dry out, the plastic insulators can crack, and the steel half can still rust. After fifteen or twenty years many have failed quietly.
Where dissimilar metals meet in Laguna Niguel homes
Most homes here were built from the 1970s through the 1990s in neighborhoods like Beacon Hill, Marina Hills, Rancho Niguel and Bear Brand. Common trouble spots include:
- Water heater inlet and outlet connections.
- Older homes where a section of galvanized pipe was tied into copper during a past repair.
- Brass valves and steel pipe at the main shutoff or pressure regulator.
- Hose bibs and exterior stubs where different materials were mixed.
Warning signs
- Crust or green buildup around a fitting.
- Rust-colored water from the hot side only.
- A slow drip at the top of the water heater.
- Reduced flow from a connection that has narrowed with corrosion.
How a repipe takes care of it
During a whole-house repipe we replace the supply piping from the main to every fixture. At the water heater we install new connectors with proper isolation, so the new system starts without any copper-to-steel contact points. PEX-A itself does not conduct electricity, which removes most dissimilar-metal joints inside the walls altogether. Laguna Niguel requires a permit and inspection for repiping and water heater work, and Moulton Niguel Water District serves most of the city.
Related reading
If your new lines will run overhead, read about repiping through the attic, and compare materials in PEX vs copper. Neighbors can visit Aliso Viejo, Laguna Hills and Dana Point, or see all cities at repipeinc.com.
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Repipe OC, 23821 Hillhurst Drive, Laguna Niguel, CA 92677, (949) 524-2362, CSLB #1087885 C-36.
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Written by Repipe OC · CSLB #1087885 C-36 · 23821 Hillhurst Drive, Laguna Niguel, CA 92677 · (949) 524-2362