Symptoms
- Drip or seepage at a specific threaded joint
- Leak is localized to one fitting rather than spread across the tank
- May worsen slightly when hot water is used, from thermal expansion
- Fitting may show mineral crust or corrosion
Likely causes
- CommonLoosened threaded fittingThermal cycling over years can gradually loosen threaded connections.
- CommonDeteriorated thread sealant or tapeOld pipe dope or tape can dry out and lose its seal.
- PossibleCorroded dielectric union or nippleThese connectors between dissimilar metals are common failure points.
- PossibleCross-threaded or improperly installed fittingA fitting installed at an angle rarely seals well even when tightened.
What to do
- Shut off the cold water supply to the tank and relieve pressure by opening a hot water tap.
- Dry the fitting completely and identify the exact leak point.
- If the fitting simply needs tightening, use two wrenches, one to hold the pipe steady and one to turn the fitting, to avoid twisting other connections.
- If tightening doesn't stop it, the fitting will likely need to be disassembled, cleaned, re-taped with thread sealant tape, and reassembled.
- Check for corrosion on the fitting itself; a heavily corroded fitting should be replaced rather than resealed.
- Restore water supply slowly and check the fitting again under normal pressure before considering it fixed.
Tools and parts
- Two adjustable wrenches or pipe wrenches
- Thread sealant tape
- Towels
Dielectric union or nippleSearch: “water heater dielectric union replacement”
When to call a pro
If a fitting is heavily corroded, hard to access, or the leak continues after resealing, a plumber can replace it properly.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.