Water Heater Leaking? Where It's Coming From and What to Do

In South Bay homes, a leaking water heater isn’t always a dead one: where the water comes from tells you how serious it is. Drips from the pipe fittings on top, the drain valve or the relief valve are usually repairable; water seeping from the tank itself means the tank has failed and the heater needs replacing.

On gas heaters, some water under the heater can be harmless condensation that stops once the tank is hot. This guide for San Jose and South Bay homeowners covers what to do first, how to find the source safely, and when to call a licensed plumber.

Safety first. Never cap, plug or remove the temperature and pressure (T&P) relief valve or its discharge pipe to stop a drip: the valve is what keeps an overheated or over-pressurized tank from bursting, and A.O. Smith warns that a tank whose valve doesn't work can explode. Water from the valve can be scalding, so keep your hands and face clear of the pipe's outlet. If water has reached outlets, cords or the electrical panel, don't walk through it to get there. If you smell gas near the heater, leave and call 911 and PG&E from outside.

What Should You Do First When a Water Heater Leaks?

1. Turn off the heater’s energy. For an electric heater, switch off its breaker. For a gas heater, turn the gas shutoff valve on the line to the heater to off (the handle crosses the pipe), or set the control knob to Off. An electric tank shouldn’t heat while it may be losing water.
2. Close the cold-water supply. The valve is on the cold pipe going into the top of the heater. If it won’t turn, or the leak keeps going, close the main water shutoff for the house.
3. Protect what’s nearby. Move boxes, wipe up the water and put down towels so you can see where fresh water appears.
4. Leave the tank alone. Draining a tank full of hot water is a scalding risk and usually isn’t needed to stop a leak once the supply is closed.
5. Call a plumber. If water is spreading into walls, ceilings or floors, call our 24/7 line.

Where Is the Water Heater Leak Coming From?

Dry everything, then look for the highest wet spot: water runs down, so the source is usually above where it collects.

Checked October 2026 against the A.O. Smith sources listed at the end.

Leaks From the Top of the Water Heater

The hot outlet and cold inlet pipes connect at the top, often through flexible connectors or short steel nipples that corrode over time. Look for wet threads, green or white crust, or rust streaks running down the jacket. A.O. Smith notes that tightening a loose connection sometimes solves the problem. If a fitting is corroded, have it replaced instead of tightened harder.

Leaks From the Relief Valve

The T&P valve is on the top or upper side of the tank, with a pipe running down toward the floor. Water from that pipe means the valve opened or is worn:

• A slow drip or occasional weeping usually means pressure is building in the tank. When water heats, it expands. If a pressure regulator, check valve or backflow preventer stops it from pushing back into the city line (a closed system), pressure rises until the valve relieves it. A.O. Smith says to control the water pressure and install a thermal expansion tank before replacing a dripping T&P valve, and recommends household pressure of 50 to 60 psi, never above 80.
• A large gush of very hot water means the water got too hot. A.O. Smith’s technical bulletin traces this to a malfunctioning thermostat. Turn off the heater’s power or gas and call a plumber.
• Seepage where the valve threads into the tank may only need resealing; seepage from the welded fitting itself means the heater has to be replaced.

A cheap pressure gauge that screws onto a hose bib lets you read your house pressure yourself. If it reads above 80 psi, the regulator needs attention.

Leaks From the Bottom of the Water Heater

Water around the base is the case to take most seriously. First check the drain valve: make sure it’s closed and look for drips from its spout or threads. A worn drain valve can be replaced. On an electric heater, also check around the lower element cover.

If the valve and element are dry and water keeps appearing under the heater, the tank itself is usually leaking. A.O. Smith says a leaking tank can’t be repaired and the heater should be replaced. Rust-colored water from the hot taps or rust on the bottom of the jacket often goes with it.

Is It Condensation?

Gas water heaters can make water. When a tank fills with cold water and the burner fires, combustion gases condense on the cold surfaces and drip down, sometimes sizzling on the burner. A.O. Smith’s bulletin says high-efficiency heaters condense more, and that condensation should stop once the whole tank is above about 115°F. It describes a simple test: wipe up the water, set the control knob to Pilot, wait eight hours and look again. No new water means it was condensation; water means a leak.

Heat pump water heaters also make water on purpose. ENERGY STAR notes that they cool and dehumidify the space they’re in; the moisture they pull from the air runs out through a condensate line to a drain. A clogged or disconnected line can look like a tank leak.

Can You Fix a Leaking Water Heater Yourself?

Safe to do:

• Turn off the power or gas and close the cold-water valve.
• Dry the heater and find the highest wet spot.
• Check that the drain valve is fully closed.
• Measure your water pressure with a hose-bib gauge.
• Clear a heat pump water heater’s condensate line where the manual shows how.

Leave to a licensed plumber:

• Replacing the T&P valve, the drain valve, fittings or element gaskets, which means draining a tank of hot water.
• Adding an expansion tank or adjusting or replacing a pressure regulator.
• Anything involving gas piping, the gas valve or venting.
• Replacing the heater, which in San Jose takes a permit and inspection.

Should You Repair or Replace a Leaking Water Heater?

Repair it if the leak is from a fitting, the drain valve, the relief valve or an element gasket, and the tank is sound. Replace it if the tank itself leaks, whatever its age. Our guides to the signs a water heater needs repair or replacement and the common causes of water heater failure help with the decision. Regular flushing and a yearly relief-valve test, described in our water heater maintenance tips, help a new heater last.

CPI Service prices, October 2026. Installed prices include the City permit. See water heater installation cost and leak detection cost.

What If the Water Isn’t From the Water Heater?

A wet floor near the heater isn’t always the heater. A supply pipe in the wall, a washing machine hose, a water softener or a drain line nearby can all leave water in the same spot. If the heater is dry after you’ve wiped it down and the water keeps coming, check the rest of the house with our whole-house leak check, or have the source traced with leak detection.

Water Heater Leaks in San Jose Homes

• Replacement needs a permit. In San Jose, a new water heater is installed under a permit and inspection with earthquake straps, proper relief valve piping and, where required, an expansion tank. Drain pans are among the code items we bring up to date. We pull the permit and schedule the inspection.
• Garages, closets and attics. Where the heater sits decides the damage: a garage floor shrugs off a drip that would ruin a hallway closet or the ceiling below an attic unit. A drain pan piped to a safe place limits it.
• Check the straps. After a leak, make sure the earthquake straps are still tight and the heater hasn’t shifted on its stand.
• The Air District rule. If the heater has to be replaced, the Bay Area Air District’s zero-NOx rule affects which new heaters you can buy; see Bay Area zero-NOx rules and rebates by city.

When Should You Call a Licensed Plumber?

Call when:

• water is coming from the tank itself or from under the jacket
• the relief valve drips repeatedly or discharges a lot of hot water
• the leak doesn’t stop after you close the cold-water valve
• water has reached a wall, ceiling, floor covering or the electrical panel
• your water pressure reads above 80 psi
• you smell gas (call 911 and PG&E from outside first)

CPI Service repairs and replaces water heaters throughout San Jose and the South Bay, with same-day service and a 24/7 emergency line. We’re licensed under CSLB License #1101278 (C-36 Plumbing), every job is quoted as a fixed price before we start, and our work carries a 1-year labor warranty. If you’re replacing the heater, we offer $250 off water heater installation and 0% interest financing for 12 months, subject to approval. If the heater is working but you have no hot water instead, see no hot water: what to check first. See water heater services, request a free estimate or call (408) 978-3093.

Sources

• A.O. Smith: Why Is My Water Heater Leaking?
• A.O. Smith: Technical Bulletin 15, Condensation
• A.O. Smith: Technical Bulletin 52, Leaking Temperature and Pressure Relief Valve
• A.O. Smith: Water Heater Maintenance Guide
• A.O. Smith: Is Your Hot Water Not Getting Hot? (water pressure)
• ENERGY STAR: Heat Pump Water Heaters
• PG&E: Gas Safety

Checked October 2026.