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Water heater leaking: find the source, then decide what to do
Turn off the power or gas and close the cold-water valve, then find where it is leaking. Leaks at the top fittings, drain valve or relief valve can often be repaired. A leak from the bottom of the tank itself usually means corrosion has eaten through the steel, and the heater needs replacing. (A.O. Smith)
Decide fast:
Water streaming, spraying, or near the gas burner or wiring? Treat it as an emergency. A drip at a fitting or valve? Usually a repair. A leak from the tank body? Plan a replacement and check the replacement cost guide.
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Do this first
- Shut off the energy. On an electric heater, switch off its breaker. On a gas heater, turn the gas shut-off valve so the handle is perpendicular to the pipe. Smell gas? Leave and call SDG&E at 1-800-411-7343 or 911.
- Shut off the water. Turn the cold-water shut-off valve on the pipe entering the top of the tank clockwise until it stops, or close your home's main water valve.
- Find the source. Wipe the tank and floor dry and watch. If moisture comes back within a few hours, it is a leak, not condensation. Check the top fittings, the relief valve, the drain valve and the tank bottom, in that order.
Full shutoff steps, gas safety and same-day pros: emergency water heater repair.
Where is it leaking? Leak-source table
A.O. Smith says tank leaks usually start at four points: the relief valve, the drain valve, the inlet and outlet connections, and the tank bottom (A.O. Smith).
| Where | Likely cause | Usually | Who to call |
|---|---|---|---|
| Top: pipe fittings | Loose or corroded inlet or outlet connections | Repair | Licensed plumber |
| Relief (T&P) valve | Failed valve, or water temperature set too high | Repair (valve) | Licensed plumber |
| Drain valve, near the bottom | Worn washer or loose connection | Repair | Licensed plumber |
| Side, electric heater | Failed gasket at a heating element | Repair, if the tank is sound | Licensed plumber |
| Bottom of the tank body | Corrosion through the steel | Replace | Licensed plumber |
| Damp tank, no drip | Condensation, not a leak | Wipe dry and watch | No one, if it doesn't come back |
| Tankless unit | Depends on the model and error code | Diagnose first | Tankless repair pro |
All causes in the table are from A.O. Smith's leak guide (A.O. Smith).
Water heater leaking from the bottom
A leak from the base of the tank usually means corrosion has eaten through the steel, and a corroded tank can't be repaired: it needs replacing (A.O. Smith). Before you assume the worst, check the drain valve near the bottom. A worn washer or loose connection there can drip onto the floor and look like a tank leak (A.O. Smith). Water running down from a fitting or the relief valve pipe can also collect at the base. Dry everything, then watch where new water appears first. A.O. Smith says hard water speeds up tank corrosion, and rumbling or popping sounds mean sediment has built up at the bottom (A.O. Smith).
Water heater leaking from the top
Top leaks usually come from the hot and cold pipe connections or the relief valve, and they are often repairable (A.O. Smith). Look for moisture or mineral crust where the pipes meet the tank. A.O. Smith says you can tighten loose connections if you can do it safely, but corroded fittings need professional replacement, and connections that keep loosening after you tighten them mean the parts are worn out (A.O. Smith).
Pressure relief valve leaking
A dripping temperature and pressure (T&P) relief valve means the valve has failed or the water temperature is set too high (A.O. Smith). Never cap, plug or remove it. The Whirlpool manual says a qualified person should replace a dripping or leaking relief valve (Whirlpool manual). A.O. Smith says water pressure above 80 PSI can turn a small crack into a gushing leak (A.O. Smith), so ask the plumber to check your home's water pressure too.
Expansion tank: under California Plumbing Code 608.3, a water system with a check valve, backflow preventer or other normally closed device that keeps pressure from flowing back to the water main must have a thermal expansion tank. CPC 608.4 also requires the relief valve to drain to the outside of the building (City of Menifee Building & Safety). A plumber can tell you whether your system needs one. See what the parts add to a job in the cost guide.
What leak repairs cost
These are national figures from This Old House (updated June 17, 2026), not San Diego quotes (This Old House):
- Minor repairs, including small leaks at connections and sticky relief valves: $150–$500.
- Relief valve parts on an install: $20–$200. Expansion tank, where required: $40–$150.
- Emergency or after-hours service: $200–$500 extra.
- Full replacement: $820–$3,500 installed. Water damage repair after a flood: $500–$2,500.
For San Diego permit, strapping and replacement prices, see the water heater replacement cost guide.
Repair or replace?
Repair when the leak is at a fitting, the drain valve or the relief valve and the tank itself is sound. Replace when the tank body leaks, the hot water stays rusty after flushing, or the unit is past 12 years old; A.O. Smith says to start planning a replacement at that age even if nothing seems wrong (A.O. Smith). The full decision guide is water heater repair vs replace.
Tankless water heater leaking?
Tankless units don't have a storage tank to fail, so a leak or error code needs a professional diagnosis. Write down any error code, shut off the gas or power and the water, and see tankless water heater repair in San Diego.
Licensed San Diego pros for leak repair
Every pro in our San Diego County directory is checked against public CSLB records; see how we verify. For the repair basics, read water heater repair.
Need a licensed pro to look at the leak?
See each San Diego County pro's CSLB license, bond and workers' comp, then call 2 or 3 for written quotes, or ask us for a free shortlist. It is free.
See licensed pros Get a free shortlist
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FAQs
Is a leaking water heater dangerous?
It can be. A.O. Smith says a steady stream or spraying water is an emergency, leaks near electrical parts on an electric heater are a shock hazard, and leaks near the burner or gas line on a gas heater can interfere with combustion and create a carbon monoxide risk. Small drips still cause water damage over time.
Can I still use a leaking water heater?
Not until it has been checked. A.O. Smith's first step for any leak is to cut the power or gas and shut off the water. If the relief valve is dripping, don't plug or remove it; the Whirlpool manual says a qualified person should replace a dripping or leaking relief valve.
Does homeowners insurance cover a leaking water heater?
It depends on your policy. Coverage for the heater itself and for water damage it causes varies by insurer and by how the leak happened, so call your insurer before you repair or throw anything out. Take photos of the heater, the leak and any damage first, and keep the plumber's written diagnosis.
How fast does a leaking water heater need replacing?
If the tank body is leaking, as soon as you can. A.O. Smith says a corroded tank can't be repaired and needs complete replacement. Tanks hold 30 to 80 gallons, a serious leak can flood a home within hours, and soaked drywall or flooring can grow mold within 24 to 48 hours.
Sources
- A.O. Smith, What to do when your hot water heater is leaking (checked October 24, 2026)
- Whirlpool gas water heater use and care manual (PDF) (checked October 23, 2026)
- City of Menifee Building & Safety, Water heater installation and strapping requirements (CPC 504.6, 507.2, 608.3, 608.4; California Plumbing Code 2025) (checked October 24, 2026)
- This Old House, Water heater installation cost (updated June 17, 2026) (checked October 24, 2026)
- SDG&E, Gas leaks (checked October 23, 2026)
- CSLB Check a License (checked October 23, 2026)