Water heater leaking: where it's coming from, what to do first, and the code's pan and valve rules
First shut the cold water valve to the heater and turn it off at its breaker or gas valve. Then find the source: water from the relief valve's pipe means the valve opened on high pressure or temperature; drips at the drain valve or the pipe connections point to that part; water from the tank itself means a new heater. Where a leak would cause damage, the code calls for a pan under the tank with a 3/4 inch drain (IRC P2801.6).
Anthony Hicks30+ years in construction. Updated November 5, 2026.
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What to do first
- Shut off the water at the cold water valve on the pipe into the heater.
- Turn the heater off: the breaker for an electric heater, the gas valve for a gas one. The heater’s label and manual show where.
- Move things out of the water and start drying the floor. Water that sat under the heater can wet the subfloor and walls around it.
Where the water is coming from
| Where | What to check |
|---|---|
| The relief valve’s discharge pipe | The temperature and pressure relief valve opened: it’s set to open on pressure above the system’s, up to 150 psi, or water at 210°F (IRC P2804.3, P2804.4) |
| The drain valve near the bottom | Whether the valve is fully closed and its cap tight |
| The pipe connections at the top | Each fitting and supply line, for the one that’s wet |
| The tank itself, from the bottom or the jacket | A leaking tank means a new heater |
A relief valve that discharges is doing its job; it’s the high pressure or temperature behind it that needs finding.
The code’s pan and valve rules
- A pan goes under a tank water heater wherever a leak would cause damage: metal at least 0.0236 inch thick or plastic at least 0.036 inch, at least 1 1/2 inches deep, drained by a pipe at least 3/4 inch to a waste receptor or outside, 6 to 24 inches above the ground (IRC P2801.6). A replacement heater doesn’t need a pan drain where none was there before.
- The relief valve’s pipe can’t be tied straight into the drain system; it discharges through an air gap in the same room, to the floor, the pan, a waste receptor or outdoors, ends 6 inches or less above the floor, runs by gravity, and has no valve, tee or threaded end (P2804.6.1).
- In a garage, a heater with an ignition source sits with that source at least 18 inches above the floor, unless it’s listed as flammable vapor ignition-resistant (P2801.7).
When it’s replaced
A leaking tank means a new heater. The water heater installation cost guide prices a 40 or 50 gallon gas tank and a tankless heater in your state, with the old one taken out. If water spread past the pan, the water damage restoration cost guide covers drying the floor and walls.
Common questions
Is a leaking water heater an emergency?
Water from the tank keeps coming until the supply is shut off, so shut the cold water valve and turn the heater off first, then deal with the water.
Why is my water heater leaking from the top?
Check the pipe connections, the supply lines and the relief valve at the top; whichever is wet is the source.
Why is water coming out of the relief valve pipe?
The valve opened because the pressure or temperature in the tank reached its setting. Find out why before replacing the valve.
Does homeowners insurance cover a leaking water heater?
It depends on the policy’s terms. Photograph the damage before cleaning up, and the insurer’s adjuster looks at the damage and its cause.