Water Heater Leaking? 6 Causes and How to Fix Them

Before you start

Shut off the supply first. A. O. Smith says not to attempt repairs while the heater is still powered and connected.⁠[3]

Water from the tank, the drain valve or the relief valve pipe can burn: A. O. Smith warns that water over 125°F can cause severe burns instantly. Before you drain anything, run a hot tap until the water is no longer hot.⁠[4]

Wipe the floor and the heater dry before each check, so new water leads you to the source. A gas heater also needs working CO alarms, so check where to put carbon monoxide alarms.

Find where the water comes from

Each leak point has its own fix, and two are jobs for a pro. Match where you see water on the diagram, then go to that section.

A. O. Smith places top leaks at the pipe fittings, side leaks at the temperature and pressure (T&P) relief valve, and base leaks at a likely tank failure.⁠[3] Its manual adds a rule that can save you a new heater: don't replace it until every possible water source has been checked.⁠[4]

1. 01

   Loose or corroded pipe connection on top

   CommonDIYTime: 15 min

   A nut or connector dripping where the pipes meet the tank.
   Fix it: Loose or corroded pipe connection on top →
2. 02

   T&P relief valve releasing water

   CommonDIY with careTime: 30 min

   The safety valve opens on high pressure or heat, or is wearing out.
   Fix it: T&P relief valve releasing water →
3. 03

   Drain valve open or worn out

   CommonDIYTime: 5–90 min

   A drain valve left slightly open, or one that drips when closed.
   Fix it: Drain valve open or worn out →
4. 04

   Leaking anode rod port

   Less commonDIY with careTime: 1–2 hr

   Water at the anode rod's hex head on top of the tank.
   Fix it: Leaking anode rod port →
5. 05

   Leaking gas control valve joint

   Less commonPro only

   On gas models, water where the gas valve threads into the tank.
   What a pro does: Leaking gas control valve joint →
6. 06

   Leaking tank

   Less commonPro only

   Water from under the jacket while every fitting stays dry.
   What a pro does: Leaking tank →

Rule out condensation first

Condensation looks like a leak but stops on its own. On a gas heater, burner exhaust can condense on the cold tank and drip onto the burner or the floor, most often at start-up or when the incoming water is cold.⁠[4] A. O. Smith says it should stop once the tank water is above about 110°F to 115°F.⁠[1]⁠[5] An electric tank can sweat in a warm room until the water heats up.⁠[3]

To test it, wipe up the water. On a model with a standing pilot, set the gas control to its pilot setting so the burner stays off, and check after 8 hours. A dry floor means condensation; water means a real leak.⁠[5]

Not sure which leak you have? Answer a few quick questions and the troubleshooter points you to the right section.

Leak at the pipe connections on top

On a top-connect heater, the cold inlet and the hot outlet join the tank on top. A loose nut, a worn connector or a corroded fitting can drip down the jacket and show up far from the real leak. A. O. Smith says snugging a loose fitting can fix it, but tightening too much can damage it and make the leak worse.⁠[3] In a humid room, check whether the cold pipe is just sweating.⁠[1]

1. 01

   Step 01 of 03

   Dry the top and watch for new drops

   • Time: 10 min
   • Microfiber towels
   • LED work flashlight

   Dry the pipes and fittings, then look again after 10 minutes with a flashlight. A cotton swab slid between the jacket opening and a fitting picks up water you can't see.⁠[4]

   You'll know it worked when: You can point to the one fitting where new water appears.

2. 02

   Step 02 of 03

   Snug the leaking connection a little at a time

   • Time: 5 min
   • Adjustable wrench

   Close the cold water valve. Turn the nut a small amount, check, and stop as soon as the drip stops.⁠[3]

   You'll know it worked when: The connection stays dry through an hour of normal use.

3. 03

   Step 03 of 03

   Call a plumber if the fitting is corroded or still leaks

   • Time: 5 min

   A connector crusted with corrosion, or a leak where the pipe threads into the tank, means draining the tank and rebuilding the joint. That is plumber work unless you have reworked water lines before.

   You'll know it worked when: A plumber knows which fitting leaks and what you already tried.

To slow corrosion at these fittings, A. O. Smith strongly recommends dielectric unions wherever the heater connects to copper pipe.⁠[4]

Still not fixed? Next likely cause: T&P relief valve releasing water →

Leak from the T&P relief valve

The T&P relief valve sits near the top of the tank, with a pipe running down toward the floor. It lets water out when the tank gets too hot or the pressure climbs too high. A. O. Smith says it is normally rated for 210°F and for no more than the tank's working pressure, generally 150 psi.⁠[6]

How the water comes out tells you why, according to A. O. Smith's T&P bulletin.⁠[6]

1. 01

   Step 01 of 04

   Watch how the valve releases water

   • Time: 5 min
   • LED work flashlight

   Stand to the side of the pipe's open end. Note when water appears: after heating, all the time, or only at the joint.

   You'll know it worked when: You know whether it drips at times, runs steadily, or seeps at the threads.

2. 02

   Step 02 of 04

   Measure the water pressure

   • Time: 20 min
   • Water pressure test gauge with max-reading needle (hose thread)

   A. O. Smith tests with a gauge on the drain valve; a max-reading needle shows how high the pressure climbs while the heater runs. When supply pressure is above 60 to 70 psi, it recommends a pressure-reducing valve.⁠[7]

   You'll know it worked when: You have a pressure reading to compare with the valve's rating.

3. 03

   Step 03 of 04

   Test the valve the way the manual says

   • Time: 5 min

   Make sure no one is near the pipe's end. Lift the lever a few times and let it snap back. A. O. Smith says the valve should seat properly and operate freely, and recommends this check every 6 months.⁠[4]

   You'll know it worked when: The valve snaps shut and stops dripping after the test.

4. 04

   Step 04 of 04

   Shut the water off if it won't reseat

   • Time: 5 min

   If the valve keeps releasing water, close the cold water inlet and turn off the gas or power at once. The new valve must match the tank's pressure rating and the heater's input, so have a plumber fit it.⁠[4]

   You'll know it worked when: The tank stops refilling while you wait for a plumber.

A. O. Smith says a T&P valve is not meant to handle thermal expansion again and again, and every closed system needs a properly sized expansion tank.⁠[4] A plumber fits one, plus a pressure-reducing valve if your supply pressure runs high.⁠[7]

Still not fixed? Next likely cause: Drain valve open or worn out →

Leak at the drain valve

The drain valve sits low on the front of the tank; you open it to flush out sediment. A. O. Smith's first check is that it is fully closed. If the handle can't stop the drip, the fix is a new valve.⁠[1] Water can also seep where the valve threads into the tank, and the swab test finds it.⁠[4]

1. 01

   Step 01 of 05

   Close the drain valve fully

   • Time: 2 min

   Turn the handle clockwise until it stops, as A. O. Smith's manual does before filling the tank. Remove any hose and check that the outlet stays dry.⁠[4]

   You'll know it worked when: No more drips from the valve outlet.

2. 02

   Step 02 of 05

   Check where the valve meets the tank

   • Time: 5 min
   • LED work flashlight

   Slide a cotton swab between the jacket and the valve's threads. A wet swab means the joint leaks, not the valve.⁠[4]

   You'll know it worked when: You know if the leak is at the valve outlet or at its threads.

3. 03

   Step 03 of 05

   Drain the tank before you work on the valve

   • Time: 60 min
   • Garden hose
   • 5-gallon bucket

   Turn off the power, and the gas on a gas heater. Run a hot tap until the water is no longer hot. Close the cold water inlet, run a hose from the drain valve to a drain, and open the valve, leaving the hot tap open.⁠[4]

   You'll know it worked when: The tank is empty and the cold water inlet is closed.

4. 04

   Step 04 of 05

   Fit a new drain valve

   • Time: 30 min
   • Adjustable wrench
   • Brass water heater drain valve
   • PTFE thread seal tape

   Unscrew the old valve. Wrap the new valve's threads with thread seal tape, screw it in and close it. If only the threads leaked, reseal the old valve the same way.⁠[4]

   You'll know it worked when: The new valve stays dry with the tank full.

5. 05

   Step 05 of 05

   Refill before you restore power or gas

   • Time: 15 min

   Close the drain valve and open the cold water inlet. Keep a hot tap open until water flows steadily. A. O. Smith says the tank must be full before the gas or power goes back on.⁠[4]

   You'll know it worked when: Water runs steadily from the hot tap and every joint is dry.

A. O. Smith recommends draining and flushing every 6 months to control sediment.⁠[4] DOE suggests draining a quart every 3 months, because sediment lowers efficiency.⁠[8]

Still not fixed? Next likely cause: Leaking anode rod port →

Leak at the anode rod port

The anode rod hangs in the tank from a threaded port on top. It corrodes so the tank doesn't; once it is used up, the tank starts to corrode and will eventually leak. A. O. Smith's leakage checklist also names the anode rod fitting as a leak point.⁠[4]

1. 01

   Step 01 of 05

   Confirm the anode fitting is wet

   • Time: 5 min
   • Microfiber towels

   Dry around the hex head on top. Slide a cotton swab between the jacket opening and the fitting; a wet swab means the threads leak.⁠[4]

   You'll know it worked when: A wet swab at the hex head confirms this leak point.

2. 02

   Step 02 of 05

   Shut off and relieve the pressure

   • Time: 10 min

   Turn off the gas or power. Close the cold water supply and open a hot tap to relieve the pressure.⁠[4]

   You'll know it worked when: The tank has no pressure and the burner or elements are off.

3. 03

   Step 03 of 05

   Drain about 5 gallons

   • Time: 15 min
   • Garden hose
   • 5-gallon bucket

   Use the drain valve and a hose, as in the drain valve section. A. O. Smith's anode procedure drains about 5 gallons, then closes the valve.⁠[4]

   You'll know it worked when: The water level sits below the top of the tank.

4. 04

   Step 04 of 05

   Reseal the anode rod, or fit a new one

   • Time: 30 min
   • PTFE thread seal tape
   • Water heater anode rod

   Unscrew the rod. A. O. Smith says to fit a new one if most of it is thinner than 3/8 inch or bare core wire shows along about a third or more of its length. Tape or seal the threads and screw the rod in.⁠[4]

   You'll know it worked when: The rod is back in with fresh tape or sealant on its threads.

5. 05

   Step 05 of 05

   Refill and check for leaks

   • Time: 15 min

   Open the cold supply and a hot tap to push the air out. Check for leaks, then restart the heater as its manual describes.⁠[4]

   You'll know it worked when: The port stays dry with the tank full and running.

A. O. Smith says to inspect the anode every 3 years, or every year with softened water, which wears it out faster.⁠[4]

Still not fixed? Next likely cause: Leaking gas control valve joint →

Leak at the gas control valve

On a gas heater, the gas control valve (the box or knob above the burner door) threads into the tank. Water at that joint is a leak in the fitting behind the valve, and A. O. Smith's fix is to take the valve out and reseal its threads.⁠[1] That means opening a gas connection, which the manual leaves to a qualified installer, a service agency or the gas supplier.⁠[4]

1. 01

   Step 01 of 04

   Check for a gas smell first

   • Time: 1 min

   Smell all around the heater, including near the floor, as A. O. Smith's lighting label says. If you smell gas, leave now.⁠[4]

   You'll know it worked when: No gas smell, so you can shut the heater off safely.

2. 02

   Step 02 of 04

   Turn the gas off at the shutoff valve

   • Time: 2 min

   Use the shutoff valve on the gas pipe next to the heater, only if you are confident doing so. Don't touch the gas control valve.⁠[3]

   You'll know it worked when: The gas supply to the heater is off.

3. 03

   Step 03 of 04

   Close the cold water supply

   • Time: 2 min

   Close the valve on the cold water line to the heater. Unplug the heater too if it has a power cord.⁠[3]

   You'll know it worked when: The tank stops refilling, so the leak slows.

4. 04

   Step 04 of 04

   Call a plumber or the heater's service agency

   • Time: 5 min

   Tell them where the water is and what you shut off. Don't restart the heater until the joint is fixed.

   You'll know it worked when: A qualified pro is booked to reseal the valve joint.

Water can damage gas controls in ways you can't see. If any part of the heater has been under water, A. O. Smith says not to run it and to replace it.⁠[9]

Still not fixed? Next likely cause: Leaking tank →

Leak from the tank itself

If water comes from under the jacket while every fitting above stays dry, the tank has most likely rusted through. A. O. Smith calls a leak at the base "often the first indication of a serious problem."⁠[3] A confirmed tank leak means a new heater, because a leaking tank can't be repaired.⁠[1]⁠[5]

Rule out the other sources first.⁠[4] Water from a top fitting or the T&P valve can run down inside the jacket. On an electric heater, a leaking element gasket behind a side cover can look like a tank leak, and its repair involves the element wiring.⁠[1] For leaks down low, see water at the bottom of the tank.

1. 01

   Step 01 of 04

   Turn off the gas or power

   • Time: 2 min

   Turn the gas shutoff valve off, or switch off an electric heater's breaker. If you smell gas, leave and call 911 and your gas company from outside.⁠[2]

   You'll know it worked when: The heater can no longer fire or heat.

2. 02

   Step 02 of 04

   Close the cold water supply

   • Time: 2 min

   Close the shutoff valve on the cold water line to the heater.⁠[3]

   You'll know it worked when: The tank stops refilling and the leak slows.

3. 03

   Step 03 of 04

   Limit the water damage

   • Time: 15 min
   • Microfiber towels
   • 5-gallon bucket

   Move stored items, mop up, and set towels or a bucket where water collects. Leave draining the tank to the plumber; the water inside can be scalding.

   You'll know it worked when: The water is contained and nothing valuable sits in its path.

4. 04

   Step 04 of 04

   Call a plumber about a new heater

   • Time: 5 min

   Copy the model and serial numbers from the rating plate. A. O. Smith asks for both on parts orders.⁠[4]

   You'll know it worked when: A plumber is booked with the heater's model and serial numbers in hand.

Once the anode rod is used up, A. O. Smith says the tank corrodes and eventually leaks.⁠[4] DOE says most storage water heaters last 10 to 15 years.⁠[8]

Still not fixed? See when to call a pro →

Parts and tools for this fix

Most checks need only towels and a flashlight. The parts below cover this guide's DIY repairs; match thread sizes and the anode rod to your heater's model before you buy.⁠[4]

Weighing a big repair on an older heater? Try the repair-or-replace calculator, and find your water heater's age first.

When to call a pro

Stop and call a pro when the fix involves gas, wiring, the T&P valve or the tank itself. A. O. Smith's manual leaves service to a qualified installer, a service agency or the gas supplier.⁠[4]

Tell the plumber which section matched your leak and what you already checked, and have the rating plate numbers ready.⁠[4]

Frequently asked questions