Water Heater Leaking?
Find Out Where From
Top, bottom, the pressure relief valve, or the drain valve — each one means something different, and one of them means the tank is at the end of its life. Find the source below, then read what it actually means.
One note on the diagram above: a T&P valve marked as needing attention can still be functioning exactly as designed — see “leaking from the pressure relief valve” below before assuming it has failed.
Where is it leaking from?
Locate the source first. The four most common places, and what each one usually means.
Leaking from the top
Check today- —The cold-water inlet or hot-water outlet fitting has loosened or its seal has failed
- —The temperature and pressure (T&P) relief valve is mounted near the top on most tanks, and a failing one shows up here
- —The anode rod access port, if your tank has one, has a worn gasket
What to do: Tighten a fitting only if it is finger-loose. A T&P valve doing its job — releasing pressure — is not the same as a T&P valve that has failed. See the section below before touching it.
Leaking from the bottom
Higher priority- —The tank itself has corroded through — the single most common reason for a bottom leak, and the one that ends with a replacement, not a repair
- —The drain valve is not fully closed or its seal has degraded
- —A fitting low on the tank has failed
What to do: A leak from the tank body itself does not get better. If tightening the drain valve does not stop it, the water is coming from the steel, and the tank is at the end of its life.
Leaking from the pressure relief valve
Read this first- —The valve is doing exactly what it is designed to do: releasing excess pressure or temperature before the tank becomes dangerous
- —Sediment or mineral buildup is holding the valve slightly open
- —The valve itself has failed and needs replacing
What to do: Do not disassemble it. Do not plug it. A T&P valve that never discharges is not a working valve — it is a tank with nowhere for excess pressure to go.
Leaking from the drain valve
Usually simple- —The valve was not fully closed after the tank was last drained or flushed
- —Sediment is caught in the valve seat, holding it slightly open
- —The valve washer has worn out — the cheapest and most common fix
What to do: Close it firmly by hand first. If it still weeps, the valve itself likely needs replacing — a low-cost part on most tanks.
Already burst or flooded? Cleanup first, diagnosis second
If there is standing water on the floor right now, the location diagnosis above can wait a few minutes. Do this first.
Is a leaking water heater actually dangerous?
A T&P valve that is discharging under pressure can release near-boiling water. Treat it as a real scald risk, not a curiosity to inspect up close.
Water reaching the wiring or heating elements is a genuine hazard. Shut off power to the unit at the breaker before you investigate further.
Beyond the immediate risks, an undiagnosed leak is a flooding problem. The average US water-damage insurance claim runs $13,954, and water heater failures specifically average $4,444 per incident.
Gas or electric — different failure points
Electric
The leak points specific to electric units cluster around the two heating elements — their gaskets, and the wiring connections behind the access panels. Water reaching either is the main electrical hazard on this type.
Gas
Gas units add the pilot light or burner assembly, the gas control valve, and the flue as additional components — none of which a water leak affects directly, since they are mechanically separate systems from the tank's water path.
A water leak on a gas water heater is not, by itself, a gas leak — they are separate systems. But if you smell gas as well, that is a different and more urgent problem. See what to do if you smell gas and get out.
The one part that decides how long a tank lasts
If the bottom-leak diagnosis above pointed at tank corrosion, this is why it happened — and the one piece of maintenance that would have prevented it.
The sacrificial anode rod
Every tank water heater has a metal rod that corrodes on purpose, so the steel tank does not. It depletes in roughly three to five years, faster in hard water — and once it is gone, the tank itself starts rusting from the inside, invisibly, until it leaks from the bottom.
A maintained water heater typically runs 15 to 20 years. A neglected one can rust out before it reaches 10. Replacing the anode rod is the cheapest maintenance on the entire unit and the one task that most changes the outcome.
Have a tankless unit?
None of the above applies the same way. Tankless units have no tank to corrode — see the FAQ below for how their leak points actually differ.
Step-by-step: replacing a T&P valve
Only once you have confirmed the valve itself has failed, not just discharged correctly. Match the new valve's rating to your heater's BTU rating before you start, and check your local plumbing code — some areas have specific requirements for the discharge line.
- 1Power down and let the tank coolSwitch off power at the breaker (electric) or turn the gas control to pilot (gas). Give the water time to cool if the heater has been running recently.
- 2Shut off the cold-water supplyClose the valve on the cold-water inlet line above the tank.
- 3Relieve residual pressureOpen a hot-water tap elsewhere in the house, or briefly lift the T&P valve's own test lever, until water stops flowing.
- 4Position a bucket or hose at the dischargeSome water will drain from the tank opening once the old valve is out — expect a small amount, not a flood.
- 5Remove the old valveUnscrew it from the tank fitting. A pipe wrench is usually enough; avoid excessive force on the tank's own fitting.
- 6Prepare and install the new valveApply PTFE tape or pipe joint compound to the threads, then hand-tighten and snug with a wrench — tight enough to seal, not so tight it stresses the tank fitting.
- 7Reattach the discharge tubeIt should terminate a few inches above the floor, pointed downward, and must never be capped or plugged.
- 8Restore water, then power or gasOpen the cold-water supply first and check the new valve for leaks before restoring power or gas.
Step-by-step: replacing a drain valve
Lower stakes than the T&P valve, and usually the more approachable of the two repairs. One safety note that matters more than the rest: refill the tank completely before restoring power.
- 1Power down and shut off the cold-water supplySame first steps as the T&P valve — power or gas off, cold-water supply closed.
- 2Drain the tankAttach a hose to the drain valve, run it to a floor drain or outside, and open the valve. Drain fully if replacing the valve entirely.
- 3Remove the old valvePlastic valves usually unscrew by hand; brass valves may need a wrench.
- 4Apply thread sealant and install the new valvePTFE tape or pipe joint compound on the threads, then hand-tight followed by a wrench snug.
- 5Refill the tank completely before restoring powerThis is the step worth not skipping: running an electric heating element with an empty or partially empty tank can destroy it.
- 6Check for leaks, then restore power or gasOnce the tank is full and the new valve is dry, power back on.
DIY, or call a plumber?
Reasonable to handle yourself
- — A drain valve that just needs closing firmly, or a worn washer
- — A finger-loose supply-line fitting
- — Replacing the anode rod on a schedule, before it fails
- — Replacing the drain valve, using the walkthrough above
Call a plumber
- — Any leak from the tank body itself
- — A T&P valve replacement, if any step above feels uncertain
- — Anything near live electrical connections
- — A leak you cannot trace to a specific fitting or valve
Catching it before the floor is wet
The anode rod schedule above prevents the most common cause. A sensor catches everything else — including the failures that give no warning at all.
Where it actually goes
Directly beneath or beside the tank, at the lowest point of the surrounding floor — that is where water pools first, regardless of which of the four leak points above is the source.
Alert, or alert plus shut-off
A simple point sensor tells you a leak has started. A system that pairs detection with an automatic shut-off valve can stop a slow leak before it becomes a flood at all — worth the difference if the water heater sits somewhere you would not notice quickly, like a basement or a garage.
Which system actually fits this leak
A water heater sits in one known place, which makes it one of the easiest leaks to catch early — a sensor on the floor beside the tank costs less than a single service call. If the tank is in a finished space or upstairs, a system that can shut the water off matters more than one that only alerts.
A sensor in the drip pan for around $15 each. No plumbing, no valve — it just gets loud when the pan fills.
Shuts the main off automatically. Worth it if the heater is above a finished floor and a slow drip could run for days unnoticed.
Sensors plus a valve controller with no plumber. Its sensors can trigger the valve directly, even with the internet down.
Frequently asked questions
It depends on where and how much. A T&P valve discharging under pressure can release near-boiling water — treat it as a scald risk, not a curiosity. On an electric water heater, water reaching the wiring or the elements is a real hazard; shut off power at the breaker before you investigate further. On a gas water heater, a water leak on its own is not a gas leak — but if you also smell gas, that is a separate and more urgent problem, and worth treating as one. Beyond the immediate risks, an undiagnosed leak is a flooding and structural problem: the US average water-damage insurance claim runs $13,954, and water heater failures specifically average $4,444.
Not always, but it is the most common cause and the one worth ruling in or out first. Check the drain valve — close it firmly by hand and watch for a few minutes. If the leak continues after that, the water is most likely coming from a corroded seam in the tank itself, which cannot be repaired. A leaking tank means replacement, not a patch.
No. T&P valves are factory-calibrated to ANSI Z21.22 and are not field-repairable — opening or adjusting one voids its safety certification, and a valve you have interfered with can no longer be trusted to do its one job. If it is leaking because it is genuinely faulty, replace the whole valve, matched to your heater's BTU rating. If it is leaking because it is releasing real excess pressure, the fix is addressing the pressure, not silencing the valve.
A slow weep from a drain valve can usually wait a day while you get a replacement part. A leak from the tank body, a T&P valve discharging repeatedly, or any leak near an electrical connection should not wait — shut off the water and power (or gas) to the unit and call a plumber the same day.
That depends entirely on your manufacturer's own policy, not on whether a professional did the work. Some parts, including some T&P valve replacements, are covered under warranty regardless of who installs them. Check your specific policy rather than assuming either way.
For a drain valve, generally yes — it is a low-cost, low-risk part on most tanks. For a T&P valve, it depends on your comfort level: the part itself is inexpensive, but you are working with a component whose only job is safety, on a tank that may still hold pressure and near-boiling water. If any step in the walkthrough below feels uncertain, that uncertainty is a legitimate reason to call a plumber instead — this is not a job where "good enough" is good enough.
No. A tankless unit has no tank to corrode, so the classic bottom-of-the-tank failure does not apply. Leaks on tankless units more often trace to the heat exchanger, its fittings, or the pressure relief valve most models still include — and are more often a loose connection from recent service than the unit failing outright. Still worth tracing to the actual source rather than assuming the worst.
Sources & References
- 1Temperature and pressure relief valves — code framework and field practicePlumbing code guidance (IPC/UPC), ANSI Z21.22, and plumbing trade sources · accessed 2026
T&P valves are NOT field-repairable: ANSI Z21.22 governs factory calibration of spring tension, seat geometry and probe response, and field disassembly voids the safety certification. Replacement must match or exceed the heater's BTU rating and pressure setpoint. Permit requirements vary — T&P replacement falls under permit rules in IPC/UPC jurisdictions, but many specifically EXEMPT like-for-like replacement on an existing heater. Warranty impact is set by the manufacturer's own policy, not by whether the work was DIY; some T&P replacements are covered under warranty. Separately: sustained pressure above 80 psi voids the warranty on most water heaters.
- 2Bob Vila, This Old House, Family Handyman and plumbing contractors, consistent across sources · accessed 2026
Sacrificial anode rods deplete in roughly 3-5 years, varying with water hardness and hot-water usage — not 8-12. A maintained water heater typically lasts 15-20 years; without anode replacement the tank may rust out before it reaches 10. This is the single maintenance task that most changes a water heater's lifespan.
- 3Insurance Information Institute (Triple-I), from ISO data · 2018–2022 accident years
Source for the average water damage and freezing claim ($13,954) and for water damage's share of all homeowners claims.
- 4Insurance Institute for Business & Home Safety (IBHS) · accessed 2026
Plumbing supply system failures are the leading source of residential water loss. Average cost per incident after the deductible: about $5,092 for a supply system failure, $5,584 for a toilet failure, $4,444 for a water heater failure. Note: the widely quoted '65%' figure refers to the share of plumbing supply failures caused by supply-material damage — NOT to the share of home floods caused by appliances.
- 5Mold remediation guidance — drying window after water exposureUS Environmental Protection Agency, corroborated by CDC and OSHA guidance · accessed 2026
EPA guidance recommends drying wet building materials within 24 to 48 hours specifically because mold can begin growing on damp drywall, wood and insulation in that window. This is a planning benchmark, not an exact trigger — EPA's own guidance notes it depends on temperature and humidity, and mold may occur even inside the window or may not occur outside it.
Figures on this page are quoted from the sources above. Where a number is widely repeated online but could not be traced to a primary source, it is not published here. Found something wrong? Tell us and we will correct it.