Water Heater Leaking? Causes and What to Do First

Water on the floor next to the water heater doesn’t always mean the heater is finished. It could be a loose fitting, the relief valve doing its job, or condensation. It could also be a sign of a hot water leak somewhere else in the house. Here’s how to make it safe, find the source and decide what happens next.

Make it safe first

1. Turn off the energy. For an electric heater, switch off its breaker. For gas, turn the control to off or pilot.
2. Close the cold water inlet valve. It’s on the cold pipe going into the top of the tank. This stops more water entering the tank.
3. Keep clear of hot water. Water in the tank and relief line can be hot enough to scald.
4. If water is spreading, close the main water shutoff and move belongings away. See what to do in the first hour of a water leak.

Where is the water coming from?

Dry the area and the heater with a towel, then watch where water reappears.

Where it’s wet	Likely cause	Usually
Relief valve or its discharge pipe	Tank too hot, pressure too high, or a worn valve	Repair; check the thermostat and expansion tank
Top: inlet/outlet pipes	Loose or corroded fittings or connectors	Repair
Drain valve near the bottom	Valve not fully closed or worn	Repair or replace the valve
Bottom of the tank, under the jacket	Rust through the inner tank	Replace the heater
Drips under a gas heater after it starts	Condensation from a cold tank firing up	Normal if it stops once the water is hot
Floor wet, heater dry	Another source: a nearby pipe, the washer, a drain, or a slab leak	Find the real source

The relief valve: don’t ignore it

Every tank water heater has a temperature and pressure (T&P) relief valve. It opens if the tank gets too hot or the pressure too high, to keep the tank from failing. Water from the relief pipe is a warning, not just a nuisance.

Common reasons it opens:

• Thermal expansion. Heated water expands. In a “closed” system, where a pressure-reducing valve, backflow preventer or check valve stops water flowing back to the street, that extra volume has nowhere to go. Plumbing codes require a thermal expansion tank in that situation, and a missing or failed one is a common cause of relief valve drips.
• The thermostat is set too high. The U.S. Department of Energy recommends 120°F for most homes, which also lowers scald risk and energy use (energy.gov water heating).
• High street pressure without a working pressure-reducing valve.
• A worn valve that no longer seals.

Never cap, plug or remove a relief valve. Have a plumber find out why it’s opening.

When the tank itself is leaking

If water is coming from the bottom of the tank or seeping out under the outer jacket, the steel inner tank has usually rusted through. That can’t be patched. The DOE puts the typical life of a storage water heater at about 10–15 years, and central Indiana’s hard water, which leaves sediment in the tank, tends to shorten it. Draining a bit of water from the tank once a year helps remove that sediment on a heater that’s still healthy.

Heater dry, but running constantly?

Sometimes the heater isn’t leaking at all, but it’s working far harder than it should. Signs include:

• The heater runs, or the burner fires, much more than usual
• A higher gas or electric bill along with a higher water bill
• Warm spots on the floor, often in a kitchen, bathroom or hallway
• The sound of water running under the floor with everything off

That pattern points to a hot water leak somewhere else, often under the concrete slab. Test it:

1. Turn off all water in the house and check that the water meter’s leak indicator moves.
2. Close the cold water inlet on the water heater.
3. If the meter stops, the leak is on the hot side. Leave the inlet closed and the heater off until it’s found.

See how to find a slab leak and hear water running when nothing is on for the next checks.

Finding a hidden hot water leak

A hot water leak under a slab or inside a wall is ideal for non-invasive detection. With slab leak detection, we:

• Isolate and pressure-test the hot side to confirm the leaking line
• Trace the line under the floor
• Use thermal imaging to see the warm bloom a hot water leak leaves on the floor
• Listen acoustically to pinpoint the spot, then mark it for the plumber

Your plumber then repairs it through one small opening, or reroutes the line. See slab leak repair options.

Get help

If your heater is dry but won’t stop running, or the meter moves with the hot side open, call us. We find hot water leaks across Bargersville and Johnson County, including Greenwood, Center Grove and Whiteland. For a leak in the heater itself, a licensed plumber handles the repair or replacement.