Category: Problems & Repairs

Last updated: October 2026

The average lifespan of a tank water heater is about 8 to 12 years in real-world use, and the U.S. Department of Energy (DOE) puts storage tank and heat pump water heaters at roughly 10 to 15 years. Tankless water heaters last longer, with the DOE estimating around 20 years. How long yours actually lasts depends mostly on water quality, maintenance (especially the anode rod and flushing), water pressure and installation quality.

Below you’ll find lifespans by type, the warning signs that a water heater is going out, how to read the serial number to find its age for the major brands, how to extend its life, and a simple rule of thumb for repair vs replace.

Quick reference: water heater lifespan by type

Gas tanks tend to fail a little sooner than electric tanks because the burner heats the tank bottom directly, where sediment collects, which concentrates heat and corrosion. Electric tanks have no flame, so the steel tank itself often lasts longer, though their elements may need replacing along the way.

What affects how long a water heater lasts?

• Water hardness. Hard water deposits more sediment in tanks and more scale in tankless heat exchangers. Both reduce efficiency and add stress.
• Anode rod condition. Steel tanks are lined with glass (porcelain enamel), and a magnesium or aluminum anode rod corrodes in place of the tank wherever the lining has tiny gaps. Once the anode is used up, the tank starts to rust. This is the single biggest factor in tank life.
• Maintenance. Annual flushing and periodic anode replacement can help a tank reach the upper end of its range; never-maintained units often fail early.
• Water pressure and thermal expansion. Pressure above about 80 psi, or repeated pressure spikes in a closed system without an expansion tank, flexes the tank and stresses welds and fittings.
• Temperature setting. Higher temperatures speed up corrosion and mineral deposits.
• Usage and size. A tank that’s too small for the household runs constantly. See what size water heater do I need.
• Installation and location. Poor venting, a damp location, missing dielectric fittings between copper and steel, or a unit in an unconditioned space can all shorten life.
• Warranty tier. Manufacturers sell the same tank sizes with 6-, 9-, 10- or 12-year warranties. Longer-warranty models often have larger or additional anode rods and better components, which is part of why they tend to last longer.

Signs your water heater is going out

Some of these signs mean “plan a replacement soon”; others mean “act now.” Here’s what to watch for:

Rusty hot water

If only your hot water is discolored, the problem is likely inside the heater. Fill a bucket from the drain valve; if it’s rusty, the tank is corroding. If both hot and cold are rusty, the problem may be galvanized pipes or your water supply instead.

Noise

Popping and rumbling are caused by water trapped under sediment boiling and bursting through. Flushing can help on a younger tank. On an old tank that’s never been flushed, the noise is often a sign the end is near. See how to flush a water heater, including when not to.

Leaks

Leaks from fittings and valves are repairable. Leaks from the tank body are not. Our guide to water heater leaking explains how to tell the difference and what to do immediately.

How to find the age of your water heater from the serial number

Your water heater’s age is on its rating plate, the label on the side of the tank (or on the front of a tankless unit). Many newer labels print the manufacture date directly. If yours doesn’t, the date is encoded in the serial number. Formats vary between brands and have changed over the years, so use the examples below as a guide and check against the manufacturer if the result doesn’t make sense (for example, a date after you moved in that you know isn’t right).

Bradford White year codes

Bradford White’s first letter repeats every 20 years and skips letters that could be confused with numbers (such as I, O and Q). Use the condition of the heater and when the house was built to pick the right cycle.

Month letters for Bradford White (and older A. O. Smith/State): A = Jan, B = Feb, C = Mar, D = Apr, E = May, F = Jun, G = Jul, H = Aug, J = Sep, K = Oct, L = Nov, M = Dec.

Tankless units

Tankless brands (Rinnai, Navien, Noritz, Takagi and others) use their own formats, and many print the manufacture date on the label. If you can’t decode it, the manufacturer’s customer service line can usually tell you the date from the serial number. Your installation paperwork or permit record is another good source.

How to extend the life of your water heater

1. Check and replace the anode rod. Inspect it every two to three years, or more often with hard or softened water (softened water can consume anodes faster). Replace it when it’s worn to about 1/2 inch thick or the steel core wire is showing. A new rod costs roughly $20 to $75; installing one before the original is gone is one of the cheapest ways to add years to a tank. If you have a sulfur smell, ask about an aluminum/zinc or powered anode.
2. Flush the tank once a year, or every six months with hard water, as Rheem recommends. Descale tankless units at least annually. See our step-by-step flushing guide.
3. Install a thermal expansion tank if your home has a pressure-reducing valve, check valve or backflow preventer on the main line. Many codes require one in these closed systems. Installed cost is typically $100 to $400.
4. Keep water pressure in check. Test with a hose-bib gauge. If static pressure is above 80 psi, a pressure-reducing valve protects the heater and every fixture in your home.
5. Set the temperature to 120°F. The DOE recommends 120°F for savings, and the CPSC recommends it to prevent scalds (water at 140°F can cause a third-degree burn in about 6 seconds, compared with about 5 minutes at 120°F). Lower temperatures also slow corrosion and scale.
6. Test the T&P relief valve once a year and replace it if it drips afterwards or won’t open.
7. Treat hard water. A water softener (for tanks, with attention to the anode) or a scale-reduction system can significantly slow buildup, especially on tankless units.
8. Insulate exposed pipes and, on older tanks in unheated spaces, consider an insulation blanket per the manufacturer’s instructions. Don’t cover the controls, burner access, T&P valve or top of a gas unit.
9. Keep the area clean and clear, especially around gas burner air intakes, and fix small leaks promptly.

Tankless water heater lifespan

Tankless water heaters are expected to last about 20 years, according to the DOE, and many manufacturers back their heat exchangers with longer warranties than tanks get. Because there’s no tank of standing water, there’s no tank to rust through. Their main enemy is scale. In hard water, minerals coat the heat exchanger, reducing efficiency, triggering error codes and eventually causing overheating or failure. Regular descaling and an inlet filter check are essential.

A tankless unit also has more electronics (sensors, a control board, a fan and an igniter on gas models). Those parts can fail and be replaced, which is part of why a well-maintained tankless heater can outlast two tank heaters. The trade-off is a higher upfront price. Compare the numbers in our guides to tankless water heater cost and tankless vs tank water heaters.

Heat pump water heater lifespan

Heat pump (hybrid) water heaters use a steel storage tank like a conventional unit, so the DOE gives them a similar 10- to 15-year lifespan. They add a compressor, fan and evaporator coil, and they need their air filter cleaned and condensate line kept clear. Their efficiency can make them cheaper to run than standard electric tanks. See heat pump water heater cost for prices and incentives.

Repair vs replace: a rule of thumb

Use these three questions:

1. Is the tank itself leaking? If yes, replace. There’s no safe, lasting repair for a corroded tank.
2. How old is it? A tank under about 6 to 8 years old with a failed part (element, thermostat, thermocouple, gas valve, T&P valve) is usually worth repairing. A tank at or beyond 10 to 12 years is usually worth replacing, especially if it’s a gas unit or shows rust.
3. What’s the cost ratio? A widely used industry rule of thumb, sometimes called the 50% rule, says to replace if a repair costs more than about half the price of a new heater. Another version: multiply the age by the repair cost; if the result is more than the cost of a new unit, replace. These are guidelines, not rules. A cheap thermocouple on a 12-year-old tank can still be worth fixing if you’re planning a replacement soon anyway.

Typical repair and replacement costs

Costs are national ranges from Angi and This Old House and vary by region, fuel type, venting and local code upgrades. For full breakdowns see water heater repair cost, water heater replacement cost, 50-gallon water heater replacement cost, gas vs electric replacement cost and installation labor cost.

Why replacing before failure usually saves money

When a tank fails, it often fails with water on the floor. Emergency and after-hours calls cost more, you have less time to compare quotes or consider a more efficient model, and you may face water damage cleanup. If your tank is past 10 years and showing any of the warning signs above, getting quotes now gives you control over timing and price.

FAQs

What is the lifespan of a water heater?

Most tank water heaters last about 8 to 12 years in practice, and the DOE estimates 10 to 15 years for storage tank and heat pump models. Tankless units last around 20 years. Maintenance, water quality and pressure have a big effect on where yours falls in that range.

How long do gas water heaters last compared with electric?

Gas tank water heaters typically last about 8 to 12 years, while electric tanks often last 10 to 15 years. The burner on a gas unit heats the tank bottom, where sediment collects, which tends to accelerate wear. Electric units have elements and thermostats that can fail but are inexpensive to replace.

How long does a tankless water heater last?

The DOE estimates about 20 years. Regular descaling, especially in hard water areas, is key to reaching that. Parts like sensors, fans and igniters may need replacing along the way.

Should I replace my water heater after 10 years?

Not automatically, but you should start planning. If a 10-year-old tank is working well and not leaking, many homeowners keep it while budgeting for a replacement. If it shows rust, leaks, makes loud noises or needs a costly repair, replacing it is usually the better value.

Can a water heater last 20 years?

Tankless units often do. Some tank heaters also reach 20 years, usually with soft water, moderate use, good pressure control and regular anode replacement. That’s the exception rather than the rule for tanks.

How do I know if my water heater is going out?

Common signs include water around the base, rusty hot water, rumbling or popping, running out of hot water sooner than it used to, lukewarm water, a dripping relief valve and an age above 10 to 12 years. A tank leak is the clearest sign it needs replacing.

How can I tell how old my water heater is?

Look at the rating plate on the side of the tank. Some show the manufacture date directly. Otherwise, the serial number contains the date: for example, Rheem uses month or week then year in the first four digits, A. O. Smith uses year then week, and Bradford White uses a letter for the year and a letter for the month.

What shortens the life of a water heater?

Hard water, a depleted anode rod, never flushing the tank, high water pressure, thermal expansion without an expansion tank, very high temperature settings, and an undersized unit that runs constantly all shorten a water heater’s life.

Does replacing the anode rod extend water heater life?

Yes. The anode rod corrodes so the steel tank doesn’t. Replacing it before it’s fully consumed, typically every few years, is one of the most effective ways to extend tank life. It won’t help a tank that’s already leaking.

Is it worth repairing a 15-year-old water heater?

Usually not, unless the repair is very cheap (such as a thermocouple) and you’re planning to replace it soon anyway. At 15 years, most tank heaters are past their expected life, and a new unit will likely be more efficient and more reliable.

Last updated: October 2026

To flush a tank water heater, turn off the gas or power, shut the cold water supply, connect a garden hose to the drain valve, open a hot faucet, drain the tank, then briefly turn the cold water back on to stir up and rinse out the remaining sediment until the water runs clear. Tankless water heaters aren’t drained this way; they’re descaled by pumping white vinegar or a descaling solution through the unit for up to about 45 minutes using a flush kit. Most manufacturers, including Rheem, recommend flushing once a year, or every six months if you have hard water.

This guide covers exactly how to flush a gas water heater, an electric water heater and a tankless unit, which tools you need, how often to do it, what a professional flush costs, and when you shouldn’t flush an old tank at all.

Quick reference: water heater flush at a glance

Why flush a water heater?

Every gallon of water that enters your heater carries dissolved minerals, mainly calcium and magnesium. Heating water makes these minerals come out of solution, and in a tank they settle on the bottom as sediment. In a tankless unit they form hard scale inside the narrow heat exchanger passages. Over time this causes problems:

• Rumbling, popping or crackling noises as water trapped under sediment boils on gas units.
• Lower efficiency and higher bills, because the burner or element has to heat through a layer of mineral insulation.
• Less hot water and slower recovery, as sediment takes up space and lower electric elements get buried.
• Overheating of the tank bottom, which can accelerate corrosion and shorten the heater’s life.
• Burned-out elements on electric tanks, and error codes or reduced flow on tankless units.
• Clogged drain valves that make future flushing harder.

Rheem lists rumbling or popping noises, rusty or cloudy hot water, running out of hot water faster, longer recovery times and rising energy bills as signs it’s time to flush.

Tools and supplies

For a tank water heater

• Garden hose long enough to reach a floor drain or outdoors (the drain point must be lower than the drain valve)
• Flathead screwdriver (many drain valves have a slotted stem)
• Bucket for checking the water and catching drips
• Towels and work gloves
• Optional: a brass drain valve to replace a plastic factory valve, Teflon tape, and a short-handled wet/dry vac
• Optional: a flashlight for relighting the pilot on older gas units

For a tankless water heater

• A tankless water heater flush kit: a small submersible pump, two washing-machine-style hoses and a 3–5 gallon bucket. Kits typically cost around $100–$120.
• About 3–4 gallons of undiluted white vinegar (Rinnai’s procedure calls for 4 gallons), or a manufacturer-approved descaling solution
• An extra hose or towel for the pressure relief valve area
• The owner’s manual for your model

Your tankless heater must have service (isolation) valves with purge ports on the hot and cold lines for this method to work. Most professionally installed units do. If yours doesn’t, a plumber can add a valve kit.

How to flush a gas water heater

1. Turn the gas control to “Pilot” or “Vacation.” On most gas water heaters, turning the knob on the gas control valve to Pilot or Vacation stops the main burner from firing while the tank is empty. Follow your manual; some recommend turning the control fully to Off. Never let the burner fire with the tank drained, as this can damage the heater.
2. Shut off the cold water supply at the valve on the cold inlet pipe above the tank. If there’s no valve, close the main water shutoff for the house.
3. Open a hot water faucet in a nearby sink or tub. This lets air into the system so the tank can drain freely rather than forming a vacuum.
4. Attach the garden hose to the drain valve at the bottom front of the tank. Run the other end to a floor drain, a utility sink or outside to an area where hot water won’t damage plants, a lawn or a septic system’s drain field. Remember the drain end needs to be lower than the valve.
5. Open the drain valve. Turn the handle or the slotted stem counterclockwise. A 40- or 50-gallon tank typically takes 20 to 40 minutes to empty, depending on sediment and water pressure.
6. Check the water. Every so often, fill a bucket from the hose. Expect cloudy water, sand-like grit or white flakes at first.
7. Stir up the remaining sediment. Once the tank is empty, open the cold water supply valve for 10 to 30 seconds at a time with the drain still open. The rush of water churns up sediment at the bottom. Repeat several times until the water from the hose runs clear.
8. Close the drain valve firmly by hand and disconnect the hose. Have a towel ready; a little water will spill.
9. Refill the tank. Open the cold water supply fully. Leave the hot faucet open until air stops sputtering and you get a steady stream, which means the tank is full. Then close the faucet. Running other hot taps briefly will purge air from those lines.
10. Check for leaks at the drain valve and fittings.
11. Turn the gas control back to “On” and set it to your normal temperature. If the pilot went out, relight it following the instructions on the heater’s label. Most newer heaters have a push-button igniter and a sealed combustion chamber.
12. Wait for the tank to reheat, usually 30 to 60 minutes for a gas unit.

How to flush an electric water heater

The process is almost identical to a gas unit, with one critical difference: an electric heater’s elements must never be powered when the tank isn’t full of water. A “dry-fired” element burns out within seconds.

1. Turn off the breaker for the water heater at the main electrical panel. It’s usually a double-pole breaker labeled “water heater.” Don’t rely on the heater’s thermostat setting.
2. Shut off the cold water supply to the tank.
3. Open a hot water faucet nearby to break the vacuum.
4. Connect a garden hose to the drain valve and run it to a drain or outside.
5. Open the drain valve and let the tank empty.
6. Pulse the cold water on and off with the drain open to stir up and flush the remaining sediment until it runs clear. Electric tanks often build sediment around the lower element, so take your time here.
7. Close the drain valve and remove the hose.
8. Refill completely. Open the cold supply and leave the hot faucet running until water flows with no air at all. This step is essential on electric units: the upper element must be fully submerged before you restore power.
9. Turn the breaker back on.
10. Check for leaks and allow time to reheat. Electric tanks recover more slowly than gas, often 1 to 2 hours or more for a full tank.

Tip: if your hot water is still short after flushing an electric tank, the lower element may already have failed because of sediment. Element replacement is a relatively inexpensive repair. See our water heater repair cost guide.

Quick flush vs full flush

You’ll see two approaches recommended:

• Quick (mini) flush: With everything left on, put a bucket under the drain valve and open it for a few seconds to let a few gallons out. This removes loose sediment at the very bottom and is a useful habit every few months on a tank you already maintain. It isn’t a substitute for a full flush.
• Full flush: The step-by-step process above. Do this at least once a year.

How to flush a tankless water heater

“Flushing” a tankless water heater really means descaling the heat exchanger. You’re not draining sediment; you’re dissolving mineral scale with a mild acid. The steps below follow Rinnai’s published 13-step procedure, which is similar for most brands (Navien, Noritz, Rheem, A. O. Smith). Always check your own manual, as some models have a dedicated flush mode or specific limits.

1. Turn off the power to the unit (unplug it or switch off the breaker).
2. Shut off the gas supply to the heater on gas models.
3. Close the water valves: the cold (blue) and hot (red) isolation valves on the service kit, and the main water valve feeding the unit.
4. Slowly remove the purge port caps on the hot and cold isolation valves to release any trapped pressure. Keep the small rubber sealing discs inside the caps safe.
5. Connect the hoses. Attach one hose from the pump outlet to the cold-side purge port. Attach a second hose to the hot-side purge port and put its open end in the bucket. Place the pump in the bucket.
6. Open the purge valves by turning their handles perpendicular to the main valve handles.
7. Add the solution. Pour about 4 gallons of undiluted white vinegar, or the manufacturer’s recommended descaler, into the bucket. Rinnai specifically warns against using harsh chemical cleaners.
8. Run the pump to circulate the solution through the heat exchanger and back into the bucket. Rinnai says the process can take up to about 45 minutes. Many manufacturers suggest 45 to 60 minutes; a heavily scaled unit in hard water may need longer.
9. Rinse the unit. Turn off the pump, dump the vinegar, and with the hot-side hose still draining to the bucket or a drain, open the cold isolation valve for a few minutes to flush clean water through and rinse out the vinegar.
10. Close the purge valves and disconnect the hoses.
11. Replace the purge port caps, snug but not overtightened.
12. Clean the inlet filter. Most tankless units have a small mesh filter on the cold water inlet. Remove it, rinse it and reinstall it (consult your manual for location).
13. Restore water, then power and gas. Open the hot and cold isolation valves (handles parallel to the pipes) and the main valve, then restore gas and power.
14. Purge air. Open a hot water faucet slowly and let it run until water flows steadily without spitting. Rinnai says this can take 2 to 3 minutes.

If your tankless unit throws a scale or flow error code, loses hot water at low flow, or makes unusual noises, it likely needs descaling, regardless of when it was last done. Learn more about running costs in our tankless water heater cost guide and how maintenance compares in tankless vs tank.

Choosing a tankless water heater flush kit

A basic tankless flush kit is a simple product, but a few details matter:

• Pump type: a submersible utility pump of roughly 1/6 horsepower is typical. Avoid underpowered aquarium-style pumps.
• Hoses: two lengths of washer-style hose with standard 3/4-inch garden hose thread fittings that match your purge ports.
• Bucket: 3.5 to 5 gallons, ideally with a lid to limit vinegar fumes.
• Descaler: some kits include a descaling concentrate. White vinegar works for most homes; heavy scale may need a manufacturer-approved product.

If you have very hard water, a scale-reduction cartridge or a water softener upstream of the heater can significantly reduce how quickly scale forms. Check your manufacturer’s guidance first, because some recommend specific treatment systems.

How often should you flush a water heater?

These intervals reflect guidance from Rheem, Rinnai and The Home Depot. Your manual is the final word, since some warranties require documented maintenance. If you don’t know whether you have hard water, check your city’s annual water quality report or use inexpensive hardness test strips. White crust on faucets and showerheads is a strong hint.

How much does a professional water heater flush cost?

Figures are national ranges from HomeAdvisor and Angi. A professional flush often includes useful extras: testing the T&P relief valve, inspecting the anode rod, checking the venting and gas connections, and catching early leaks. If your heater hasn’t been serviced in years, that inspection alone can be worth the price.

When NOT to flush a water heater

Flushing is routine maintenance, but there are situations where a DIY flush can do more harm than good:

• The tank is old and has never been flushed. On a heater that’s 8 to 12 years or older with years of built-up sediment, the sediment can be the only thing “sealing” thin, corroded spots. Disturbing it can expose a pinhole leak. Rheem suggests calling a professional for units in this age range. Many plumbers will advise you to skip the flush and plan a replacement instead. Find your unit’s age with our water heater lifespan guide.
• The drain valve won’t open, is cracked or leaks. Forcing an old plastic valve can snap it off, leaving you with a tank that can’t be closed. Call a plumber.
• Sediment has hardened. If almost nothing comes out of an open drain valve, the valve may be clogged with sediment. Specialized tools or a valve replacement may be needed.
• The tank is already leaking. If the tank body is leaking, flushing won’t help. See water heater leaking: what to do.
• There’s heavy rust or corrosion on the fittings, the tank bottom or the gas valve.
• You’re unsure about the gas or electrical steps. That’s a good reason to hire a pro.

If you’re facing a likely replacement anyway, get prices from our water heater replacement cost guide and check what size water heater you need before you buy.

Common flushing problems and fixes

• Water drains very slowly or not at all: Sediment is blocking the drain valve. Try closing the valve, turning the cold water on briefly to “backflush” through the hose, and reopening. If that fails, you may need a plumber or a full-port drain valve.
• Drain valve drips after flushing: Sediment is stopping it from seating. Open and close it a few times to flush the seat, or fit a brass hose cap. Replace the valve if it keeps dripping.
• Pilot won’t relight: Air may be in the gas line if the gas supply was fully shut, or the thermocouple may be weak. Follow the label instructions; if it won’t stay lit, call a pro.
• No hot water from an electric unit after flushing: The element may have been dry-fired if power was restored before the tank was full, or the high-limit reset button may have tripped. Turn off the breaker and call a professional if you’re not comfortable working on 240-volt components.
• Sputtering faucets: Air in the lines. Run each hot tap for a minute.

Other maintenance to do while you flush

1. Test the T&P relief valve. Put a bucket under the discharge pipe, lift the lever for a few seconds and let it snap back. Water should flow and then stop. If it keeps dripping, replace it.
2. Inspect the anode rod every few years. If it’s worn to less than about 1/2 inch thick or you can see the steel core wire, replace it.
3. Check the temperature setting. The DOE and CPSC recommend 120°F for most homes.
4. Look for corrosion on fittings, the drain pan and around the burner.
5. Keep the area clear of stored items, especially flammables near gas units.

FAQs

How often should I flush my water heater?

Once a year for most tank water heaters, and every six months if you have hard water or hear rumbling. Tankless units should be descaled at least once a year, and more often in hard water areas. Check your owner’s manual, because the manufacturer’s schedule takes priority.

How long does it take to flush a water heater?

A typical 40- or 50-gallon tank takes about one to two hours from start to finish, including draining, rinsing and refilling. Add reheat time: around 30 to 60 minutes for gas and one to two hours or more for electric. A tankless descale takes roughly an hour to an hour and a half.

Do I need to turn off the gas to flush my water heater?

You need to stop the burner from firing. On most units, setting the gas control to Pilot or Vacation does this. Some manuals recommend turning it fully off. Never let the burner run with the tank empty.

Can I flush my water heater without turning off the water?

You can do a quick mini-flush by opening the drain valve for a few seconds with the water on, but for a full flush you need to shut off the cold supply so the tank can drain completely. You’ll turn the cold water back on in short bursts to stir up sediment at the end.

What happens if you never flush your water heater?

Sediment builds up, which can lower efficiency, cause rumbling noises, reduce hot water capacity, burn out electric elements and overheat the tank bottom. All of this can shorten the heater’s life. Many tanks still last years without flushing, but they tend to fail sooner.

Is it too late to flush my old water heater?

It may be. If the tank is 8 to 12 years old or more and has never been flushed, disturbing heavy sediment can expose corrosion and cause a leak. In that case, have a plumber assess it, or consider budgeting for a replacement.

How much vinegar do I need to flush a tankless water heater?

Rinnai’s procedure calls for 4 gallons of undiluted white vinegar. Most flush kits use 3 to 4 gallons in a 5-gallon bucket. Don’t dilute it and don’t use harsh chemical cleaners unless your manufacturer approves them.

How long should vinegar run through a tankless water heater?

Rinnai says up to about 45 minutes. Many manufacturers and plumbers recommend 45 to 60 minutes of circulation, with longer times for heavily scaled units. Rinse with fresh water afterward.

Does flushing a water heater make it last longer?

Regular flushing removes sediment that causes overheating and corrosion on the tank bottom, which helps a heater reach the upper end of its expected life. Flushing works best alongside replacing the anode rod and controlling water pressure.

How much does it cost to have a plumber flush a water heater?

About $75 to $150 for a typical tank, rising to $180 to $250 or more for 60- to 80-gallon tanks. A tankless descale usually costs $150 to $250. Prices vary by region and whether other maintenance is included.

Last updated: October 2026

If your water heater is leaking, shut off the power or gas, close the cold water supply valve on top of the tank, and then work out where the water is coming from. Leaks from the top (pipe connections) or the drain valve are usually cheap repairs, but water coming from the bottom of the tank itself almost always means the tank has corroded through and needs to be replaced. A leak from the temperature and pressure (T&P) relief valve can be a sign of dangerous pressure or temperature, so it should never be ignored or plugged.

This guide walks you through the exact shutoff steps, how to diagnose a leak by its location, what each repair typically costs, and when a leaking water heater is a genuine emergency.

Quick reference: water heater leak by location

Is a leaking water heater dangerous?

Most leaks are not immediately dangerous to people, but some are, and all of them can cause expensive water damage if left alone. The risks fall into four groups:

• Gas leaks. A gas water heater that is leaking water can also have a damaged gas line, flue or burner assembly. If you smell rotten eggs or sulfur, that is a gas leak, not a water leak, and it takes priority over everything else (see the warning below).
• Electrical shock. Electric water heaters run on 240-volt circuits. Water pooling around an electric unit, its junction box or a nearby outlet creates a shock risk. Do not stand in water and touch the heater or its wiring.
• Scalding. Water inside the tank can be 120°F to 140°F or hotter, and much hotter if the thermostat has failed. The U.S. Consumer Product Safety Commission (CPSC) notes water at 140°F can cause a third-degree burn in about 6 seconds, and at 150°F in about 2 seconds.
• Pressure. A T&P relief valve that is discharging is doing its job: releasing excess pressure or heat. If the valve has been capped, plugged or has seized, a tank can fail violently. Never cap a relief valve or its discharge pipe.

What to do if your water heater is leaking: step by step

Work through these steps in order. They take about 10 minutes and will stop most leaks from getting worse while you figure out the cause.

1. Check for a gas smell first. If you smell gas, stop and follow the warning above.
2. Cut the energy supply.
   • Electric: Switch off the water heater’s double-pole breaker (usually labeled “water heater” or “WH,” often 30 amps) at the main panel. If you have to stand in water to reach the heater’s own disconnect, use the breaker panel instead.
   • Gas: Turn the gas control knob on the front of the heater to “OFF” (or “Pilot” if you plan to restart soon). For a full shutoff, turn the handle on the gas supply line so it sits perpendicular (crosswise) to the pipe.
3. Shut off the cold water supply. Find the valve on the cold water inlet pipe at the top of the tank (usually marked with blue or on the right side as you face the unit) and turn it clockwise until it stops, or a quarter turn for a lever-style ball valve. If that valve won’t close or there isn’t one, close the main water shutoff for the house.
4. Relieve the pressure. Open a hot water faucet somewhere in the house. This drops the pressure in the tank and can slow or stop a leak from fittings or the relief valve.
5. Contain the water. Move valuables, boxes and rugs away. Put down towels or use a wet/dry vac. If the heater is in an attic, closet or upper floor, check the ceiling below.
6. Dry the tank and find the source. Wipe the tank, pipes and valves completely dry with a towel, wait 10–20 minutes, and look for where water reappears first. Water runs down, so a bottom leak may start at the top.
7. Decide whether to drain the tank. If water is coming from the tank body itself (not a fitting or valve), the tank will keep leaking until it is empty. Attach a garden hose to the drain valve, run it to a floor drain or outside, and open the valve. Be careful: the water will be hot.
8. Call a plumber if the leak is from the tank, the T&P valve keeps discharging, you can’t shut off the water, or the unit is gas and you’re not comfortable working around it.

Why is my water heater leaking? Causes by location

The location of the water is the single best clue to the cause, and to whether you’re looking at a repair or a replacement. Start at the top of the heater and work down.

Rule out condensation first

Not every puddle is a leak. Manufacturers including A. O. Smith note that condensation can form when cold incoming water (especially in winter) cools the tank, and on gas units when the burner fires and moisture in the combustion gases condenses on the cold tank or flue. This “sweating” can drip onto the burner and even make a sizzling sound. Condensation is typically temporary and stops once the water in the tank heats up. If the floor is dry after the tank has been at temperature for a few hours with no large hot water draws, condensation is the likely culprit. If water keeps appearing, it’s a real leak.

Water heater leaking from the top

Leaks at the top are the most common and usually the cheapest to fix. Check these spots:

• Cold inlet and hot outlet connections. The pipes connect to the tank with threaded nipples, often through flexible connectors. Thermal expansion and contraction can loosen them over time, and dissimilar metals (copper on steel) can corrode. A slightly loose compression nut may just need a gentle snug-up with a wrench. Don’t overtighten; that can crack fittings and make things worse. A corroded nipple or flex line needs to be replaced.
• Cold water shutoff valve. The packing nut behind the valve handle can drip. Tightening the packing nut an eighth to a quarter turn often stops it; otherwise the valve needs replacing.
• Anode rod port. The anode rod screws into the top of the tank (on some models it’s combined with the hot outlet). If the fitting has corroded or the seal has failed, water seeps out around it. Replacing the anode rod with new thread sealant usually fixes it.
• T&P valve (top-mounted). On some heaters the relief valve is on top. See the relief valve section below.
• Tank top seam. If water is seeping from under the top cover itself rather than from a fitting, the tank may be failing at the top. That’s a replacement.

Water heater leaking from the relief valve

The T&P (temperature and pressure) relief valve is the brass valve with a lever, usually on the side or top of the tank, with a pipe running down toward the floor. Residential valves are commonly rated to open at 150 psi or 210°F; the exact rating is printed on the valve’s tag. A relief valve leaking or discharging points to one of these causes:

• Thermal expansion. Water expands as it heats. If your home has a pressure-reducing valve, a check valve or a backflow preventer on the main line (common with newer water meters), that extra volume has nowhere to go and pressure spikes during every heating cycle. The usual fix is a properly sized and pre-charged thermal expansion tank, which many local codes require on these “closed” systems.
• High street pressure. Household water pressure above 80 psi is generally too high, and plumbing codes typically require a pressure-reducing valve above that level. A $10–$15 hose-bib pressure gauge will tell you your pressure in a minute.
• Overheating. A thermostat set too high or a failed thermostat can push water toward the valve’s temperature limit. If the water at your taps is dangerously hot or you hear the tank boiling or rumbling, turn off the power or gas and call a plumber.
• A worn or dirty valve. Sediment or mineral scale can stop the valve from seating properly after it opens, so it drips constantly. Replacing the valve is a modest repair (about $20 for the part, up to around $200 with a plumber, according to Angi).

Water heater leaking from the bottom

This is the scenario most homeowners search for, and it has two very different outcomes depending on exactly where the water is coming from.

1. The drain valve. The drain valve sits near the bottom front of the tank and looks like a hose spigot. If it’s dripping from the spout, it may not be fully closed, or debris from sediment may be stopping it from sealing. Try closing it firmly by hand. Many factory valves are plastic and can crack or wear. A temporary fix is a brass garden hose cap screwed onto the outlet; the real fix is replacing the valve with a brass one, which requires draining the tank. This is a small repair.

2. The relief valve discharge pipe. The T&P discharge pipe ends near the floor, so a dripping relief valve can look like a “bottom” leak. Check the end of the pipe. If it’s wet, go back to the relief valve section.

3. The tank itself. If water is coming from under the tank, from the burner compartment on a gas unit, or from beneath the jacket (outer shell) on an electric unit, and you’ve ruled out the drain valve, discharge pipe and condensation, the inner steel tank has almost certainly corroded through. Tanks are protected by a glass lining and a sacrificial anode rod, but once the anode is used up, corrosion attacks the steel. Sediment buildup on the bottom accelerates this, particularly on gas units where the burner heats the tank bottom. A corroded tank cannot be repaired. The leak will get worse, sometimes suddenly. Drain the tank and plan a replacement.

Leaking from the electrical access panels (electric)

Electric tanks have one or two access panels covering the heating elements and thermostats. Water behind these panels can come from a leaking element gasket, which is repairable when the element is replaced. If it’s coming from the tank wall around the element, the tank is failing. Always turn off the breaker before removing an access panel and confirm it’s dead with a non-contact voltage tester.

Tankless water heater leaking

Tankless leaks are usually at the water connections, isolation valves, pressure relief valve or heat exchanger. On condensing models, a clogged or disconnected condensate line can also look like a leak. A leaking heat exchanger is a major repair; check the warranty, which is often longer than a tank’s. See our guide to tankless water heater cost.

Water heater leak repair costs

Prices vary by region, unit type and whether you need an emergency call-out. The ranges below are typical national figures from cost guides such as Angi and This Old House; they’re a guide, not a quote.

Plumber labor typically runs $50 to $150 per hour, and many plumbers charge a flat service-call fee. After-hours, weekend and holiday calls cost more. For a detailed breakdown of individual repair prices, see our water heater repair cost guide.

Repair or replace a leaking water heater?

Use the leak location and the heater’s age together to make the call.

Repair it if:

• The leak is from a fitting, valve, anode port or heating element gasket, and the tank itself is dry.
• The heater is less than about 8 years old and otherwise working well.
• The relief valve is discharging because of pressure that an expansion tank or pressure-reducing valve will solve.
• The repair is a small fraction of replacement cost.

Replace it if:

• The tank itself is leaking. This is the one situation with no repair option.
• The heater is 10 years or older (most tank heaters last roughly 8 to 12 years in practice; the U.S. Department of Energy cites about 10 to 15). See our water heater lifespan guide for how to find your unit’s age from the serial number.
• You see rust in the hot water, rust on the tank bottom, or heavy corrosion on the fittings.
• The repair would cost more than about half the price of a new heater on an older unit. This “50% rule” is a common industry rule of thumb, not a hard law.

If you’re replacing anyway, it’s a good moment to reconsider size and type. Our guides cover water heater replacement cost, 50-gallon replacement costs, gas vs electric, tankless vs tank, heat pump water heaters and what size water heater you need. Labor and code upgrades (expansion tank, drain pan, earthquake straps in some states, venting) can add significantly to the price; see installation labor costs.

When is a leaking water heater an emergency?

Call a plumber (or your gas utility) right away if any of these apply:

• You smell gas or rotten eggs near the heater.
• Water is near the electrical panel, outlets or the heater’s wiring and you can’t safely shut off the breaker.
• The T&P valve is spraying or discharging continuously, or the tank is making loud banging, boiling or hissing sounds.
• You can’t stop the water: the cold water shutoff won’t close and you can’t find the main shutoff.
• The heater is in an attic, upstairs closet or finished space where a leak will damage ceilings and floors.
• Water is pouring rather than dripping from the bottom of the tank.
• The tank is bulging or visibly deformed.

A slow drip from a fitting or drain valve can usually wait for a scheduled appointment once the water is off. A drip from the tank itself is urgent: tank leaks get worse, not better.

How to prevent water heater leaks

1. Flush the tank once a year (every six months with hard water) to remove sediment that corrodes the tank bottom. Here’s how to flush a water heater safely.
2. Check the anode rod every few years and replace it before it’s down to the core wire.
3. Test the T&P valve once a year by lifting the lever briefly, with a bucket under the discharge pipe. If it won’t reseat and keeps dripping, replace it.
4. Check your water pressure and install an expansion tank if you have a closed system.
5. Keep the thermostat at about 120°F, the setting recommended by the DOE and CPSC for energy savings and scald prevention.
6. Install a drain pan and a leak alarm (or an automatic shutoff valve) so a leak becomes a minor cleanup, not a disaster.

FAQs

Why is my water heater leaking from the bottom?

The most common causes are a drain valve that isn’t fully closed or has worn out, a dripping T&P relief valve whose discharge pipe ends near the floor, condensation, or a corroded tank. Check the drain valve and discharge pipe first. If both are dry and water is coming from under the tank, the tank has likely rusted through and needs replacing.

Is a leaking water heater dangerous?

It can be. A small fitting leak is mainly a water-damage risk, but leaks can also create shock hazards around electric units and scalding risks from very hot water. A relief valve that discharges repeatedly signals high pressure or temperature. If you smell gas, leave the home and call your gas utility or 911 from outside.

Can I still use my water heater if it’s leaking?

It’s best not to. If the leak is from a fitting or valve, you can sometimes use the heater after a proper repair. If the tank itself is leaking, shut off the water and energy supply and drain it, because the leak will worsen and could release a large amount of water.

How long can a water heater leak before it bursts?

There’s no reliable timeline. A pinhole leak in a corroded tank may drip for days or weeks, or the weakened steel can fail suddenly. Because you can’t predict it, treat any tank leak as a reason to replace the unit promptly.

Can a leaking water heater be repaired?

Yes, if the leak is from a fitting, the drain valve, the relief valve, the anode port or an element gasket. No, if the leak is from the tank itself. Corrosion inside the tank can’t be patched in a way that is safe or lasting.

Why is my water heater leaking from the pressure relief valve?

Usually because of high pressure from thermal expansion in a closed system, high incoming water pressure (above about 80 psi), water that’s too hot, or a worn valve that won’t reseat. An expansion tank, a pressure-reducing valve or a new relief valve typically solves it. Never plug the valve.

Why is my water heater leaking from the top?

Most top leaks come from loose or corroded inlet and outlet connections, a dripping shutoff valve, the anode rod fitting, or a top-mounted relief valve. These are usually inexpensive repairs. Water seeping from beneath the top cover with no fitting involved can indicate a failing tank.

Is it normal for a water heater to have water underneath it?

A little moisture from condensation can be normal, particularly on gas units when cold water enters the tank. It should stop once the water is hot. Ongoing puddles are not normal and point to a leak.

How much does it cost to fix a leaking water heater?

Simple fixes like tightening fittings cost little or nothing. Replacing a relief valve runs up to about $200, an expansion tank $100–$400, and the average water heater repair is around $616 nationally. If the tank is leaking, expect to pay roughly $1,200 to $3,500 or more for a replacement.

Does homeowners insurance cover a leaking water heater?

Policies usually cover sudden water damage to your home caused by the leak, but not the cost of the water heater itself, since that’s considered wear and tear. Long-term leaks you didn’t address may not be covered. Check your policy and document the damage.