Water Heater Flush: How to Flush Gas & Electric Tanks

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Quick answer from a licensed plumber: To flush a tank water heater, turn off its heat first (the breaker for an electric heater; the gas control and the manual gas valve for a gas heater), then let the hot water cool or run a hot faucet until it does. Close the cold supply, run a hose from the drain valve to a drain, open the valve and let the tank empty. Run cold water through until it comes out clear, close the drain, and refill the tank completely before you restore power or gas. Full steps are below.

How often depends on the maker. A. O. Smith’s gas manuals say every 6 months, and its electric guide says after the first six months, then at least once a year. Rheem’s manuals suggest a few quarts every month, and Bradford White’s list a gallon a month. Rheem’s website says once a year, or every 6 months with hard water. Read your own manual; the makers’ wording is under How often, below.

Two safety rules from all three makers. The water you drain can scald. And never turn the heat back on until the tank is full. Rheem says its warranty does not cover damage from running an empty or partly empty tank, and Bradford White says its warranty does not cover electric elements that fail from dry-firing.

A tankless heater has no tank to flush. It needs descaling, which is a different job: how to descale a tankless water heater.

Relief valve dripping after a heating cycle? That is usually thermal expansion — see expansion tanks.

What you need

Your heater’s manual. A. O. Smith and Bradford White both point you to the manual for your model, and the three makers do not agree on every detail (see below).
A garden hose long enough to reach a floor drain or the outdoors, or buckets. Every maker guide I read drains the tank through a hose on the drain valve. The drained water can be hot, so if you are buying one for this, the Amazon listing for the Gilmour Pro rubber hot water garden hose (5/8 in. x 25 ft) says it is rated for use up to 180°F.
Thick gloves and safety goggles. A. O. Smith recommends both while you drain the tank.
Old towels or rags for spills, as A. O. Smith suggests.
A flathead screwdriver. Some drain valves open with a screwdriver in the slot, per A. O. Smith and Bradford White.
Time. A. O. Smith suggests turning the heater off a few hours before you drain it so the water cools.

How to flush a water heater, step by step

These steps combine the drain-and-flush sections of the A. O. Smith, Rheem and Bradford White manuals listed under Sources. Where the makers differ, I say so.

Turn off the heat.
- Electric: switch the heater’s circuit breaker OFF (A. O. Smith). Rheem says to shut off the power before draining and Bradford White says to disconnect it.
- Gas: turn the gas control to OFF and close the manual gas shut-off valve (A. O. Smith). Rheem says to shut off the gas at the gas control, gas cock or manual shut-off valve before draining. Bradford White has you turn the thermostat dial to its lowest setting, turn the gas control knob to OFF (on its White Rodgers mechanical control) and shut off the gas supply.
Let the water cool. Open a hot faucet nearby and let it run until the water is no longer hot. A. O. Smith warns to be sure the water runs cool before draining, to reduce the risk of scalding. Rheem and Bradford White both warn that the drained water may be hot. Wear the gloves and goggles.
Close the cold water supply valve to the heater.
Connect a garden hose to the drain valve and end it at an adequate drain, outdoors, or in buckets (A. O. Smith). Secure the hose end so it cannot whip loose; A. O. Smith’s gas manual says to secure the hose before and during the whole flush.
Open a hot faucet, then the drain valve. Open a hot water faucet so the tank can drain (A. O. Smith, Rheem and Bradford White all list this). Open the drain valve, with a screwdriver in the slot if yours has one; Bradford White turns it counterclockwise, by the knob on its gas models and by the screwdriver slot on its electric models. Rheem’s manuals and a Bradford White bulletin also list opening the relief valve to let air in. I skip that: Bradford White warns that when you lift the relief valve lever, hot water is released under pressure, and Rheem warns to make certain no one will be exposed to the hot water the valve releases, which may be hot enough to scald and should go to a suitable drain.
Let the tank empty, then flush out the sediment. With the drain open, turn the cold supply back on and let the water run until no more sediment comes out (A. O. Smith). A. O. Smith’s gas manual adds a caution for this step: the water will be hot. It says to secure the hose before and during the flush, which runs with system water pressure applied to the heater.
Close the drain valve and remove the hose.
Refill the tank. With the drain closed, leave a hot faucet open and open the cold supply. Keep the hot faucet running for at least three minutes after the water runs steadily, so the air is out (A. O. Smith), then close it. Check the drain valve, the relief valve and the water connections for leaks (Bradford White).
Restore the heat only after the tank is full.
- Electric: turn the breaker back on. A. O. Smith says not to restore power until the tank is completely full, and that skipping the three-minute air purge can burn out the upper element. Rheem says not to turn the heater on unless it is filled with water, or if the cold water supply shut-off valve is closed. Bradford White says that heating elements not fully under water can fail, and that dry-firing is not covered by warranty. A. O. Smith says the tank may take two hours to heat.
- Gas: open the manual gas valve and relight following the lighting instructions on the heater’s label. A. O. Smith cautions not to turn on the gas unless the tank is full. Its gas manual also says a cold tank can drip condensation onto the burner while it warms, which is not a tank leak. Bradford White’s gas manual warns to wait at least 2 minutes after the gas control is pressurized with gas before you light the pilot or push the igniter button; failing to do so may result in severe injury.

A note on “Pilot.” Some instructions say to turn a gas heater’s dial to Pilot for a flush, and a Bradford White tech bulletin says the same. The manuals I opened say something different: OFF at the gas control and the gas supply shut. That is what the steps above follow.

While the heater is open, check whether it is time to replace the anode rod — the part that decides how long the tank lasts.

How often to flush a water heater

The makers do not agree, so use the interval in your own manual. What the ones I read say:

A. O. Smith. Its gas manuals recommend draining and flushing the tank every 6 months. Its electric guide says to do it after the first six months, then, depending on the hardness of your water, at least annually or more often. A. O. Smith’s website says most tank heaters need flushing at least once a year, more often in hard water, and to defer to your manufacturer’s handbook.
Rheem. Its use-and-care manuals suggest draining a few quarts from the tank every month. Rheem’s website says to flush once a year for most households, and every 6 months if you have hard water.
Bradford White. Its gas and electric manuals list draining off a gallon each month to remove silt and sediment. That list is written for a qualified service technician. The electric manual also says to drain the heater at least once a month through the drain valve until the water runs clear. A Bradford White bulletin, quoting the Air-Conditioning, Heating and Refrigeration Institute, says to flush the tank each time you check the pressure relief valve.

So a quick monthly draw-off and a full flush are different routines, and the makers set them differently. If your tank has never been flushed and is several years old, Rheem warns that hardened sediment on older tanks or tanks not flushed in a while can be hard to remove without specialized tools, and that trying it yourself could lead to leaks or further damage. If you are unsure, bring in a pro. On hard water, see hard water signs and fixes.

On a Richmond electric tank, the EverKleen name does not replace the applicable maintenance instructions. Our Richmond model and warranty guide identifies the linked Essential and Encore manual revisions, their upkeep guidance and the records to keep for service.

For a State unit, keep the exact manual with its model and serial number. Our State water heater document guide explains the linked electric manual’s maintenance schedule, model-specific dimensions and warranty checks. Confirm that the manual applies to your heater before arranging service.

Why flushing matters

A. O. Smith’s gas manual says sediment in the bottom of the tank makes noise and may cause premature tank failure.
A. O. Smith’s electric guide says minerals in tap water can form lime deposits on the heating elements or sediment in the bottom of the tank, and that draining sediment extends the life of the tank, the elements and the drain valves.
Rheem says the sediment layer acts like insulation, so the heater runs longer heating cycles and uses more energy, and that rumbling and popping are often caused by sediment that flushing can remove.

If the tank won’t drain, or the drain valve leaks

On a neglected heater, sediment can clog the drain valve or form masses that stop the tank draining. A. O. Smith says to call a plumber or service technician if you cannot flush the tank, and its electric guide says to have a qualified person use a de-liming agent suitable for potable water. Don’t force the valve.

If sediment keeps clogging the drain valve, some people use a flushing tool made for tank heaters. Rheem’s warning above about older tanks and tanks not flushed in a while still applies. The Sediment Buster flushing tool’s Amazon listing says it runs from a CO2 cartridge, an air compressor or a hand pump (sold separately) and has a see-through window and a full-port design.

The A. O. Smith, Rheem and Bradford White documents I read do not mention this kind of tool, so follow the tool’s own instructions and your heater’s manual. The best water heater flush kit guide compares it with the tankless pump kits.

If the drain valve drips after you close it, A. O. Smith’s gas manual has a washer replacement: turn off the gas, drain the tank, unscrew the hex cap below the handle, swap the washer, tighten the cap without over-tightening it, refill, and check for leaks. Replacing the whole valve also means draining the tank first.

The Rheem PT16830C brass full flow drain valve’s Amazon listing gives the size as 3/4 in. NPT, says it is a direct replacement for Rheem, Ruud and Richmond heaters and fits most other brands, including A. O. Smith, Bradford White and State, and tells you to confirm fitment with your equipment manual. Compare it with the valve on your tank before you buy.

If draining barely moves or the tank is old, it may be near the end anyway; see how to replace a water heater and my best water heater picks. And if you spot water pooling at the base during this, that is a separate problem — here is why a water heater leaks.

Tankless heaters need descaling, not flushing

A. O. Smith says a tankless heater does not need flushing because it has no storage tank, but that many need descaling. Rheem says a tankless heater needs periodic descaling instead of flushing. Descaling uses a pump, a bucket and a descaling solution, so follow how to descale a tankless water heater rather than the steps above.

If your tank is popping or rumbling, that is sediment, see what a noisy water heater means and how to quiet it.

Frequently asked questions

How often should I flush my water heater?

It depends on the maker, so check your manual. A. O. Smith’s gas manuals say every 6 months, and its electric guide says after the first six months and then at least annually, depending on water hardness. Rheem’s manuals suggest draining a few quarts every month, and its website says once a year, or every 6 months with hard water. Bradford White’s manuals list draining a gallon a month.

Can I flush my water heater myself?

Many people do. A. O. Smith says a flush is manageable if you understand the correct procedure for your unit, and Rheem says it is manageable for many homeowners but recommends a professional for older units or heavy buildup. Rheem also says to call a professional if you are unsure about handling gas or electrical components.

Do I turn the water heater off before I flush it?

Yes. For an electric heater, switch off the breaker before you drain it. For a gas heater, turn the gas control to OFF and close the manual gas shut-off valve, as the A. O. Smith and Bradford White gas manuals say. Then let the hot water cool or run a hot faucet until it does, because the water in the tank can scald.

Why won’t my water heater drain when I flush it?

Sediment can clog the drain valve or form large masses in the tank. A. O. Smith says to call a plumber or service technician if you cannot flush the tank, and its electric guide says to have a qualified person use a de-liming agent suitable for potable water. Do not force the valve.

Can I turn the heater back on before the tank is full?

No. A. O. Smith says not to turn an electric heater’s power back on until the tank is completely full of water, and that skipping the air-purge step can burn out the upper heating element. Its gas manual says not to turn on the gas unless the tank is full. Rheem says the same, and that its warranty does not cover damage from running an empty or partly empty tank. Bradford White says its warranty does not cover electric elements that fail from dry-firing.

What happens if I never flush my water heater?

Sediment builds up in the bottom of the tank. A. O. Smith’s gas manual says it makes noise and may cause premature tank failure, and Rheem says the layer acts like insulation, forcing longer heating cycles and using more energy. On an electric heater, A. O. Smith says minerals can also form lime deposits on the heating elements.

Is flushing a tankless water heater the same job?

No. A. O. Smith says a tankless heater does not need flushing because it has no storage tank, but that many need descaling, and Rheem says a tankless heater needs periodic descaling instead of flushing. Descaling is a different procedure, with a pump, a bucket and a descaling solution. See how to descale a tankless water heater.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. The steps, warnings and intervals on this page come from the maker manuals and pages listed below, which I opened and read on September 29, 2026; nothing here is from hands-on testing. Each linked product was shown as in stock on Amazon on September 29, 2026. Where a link goes to Amazon we may earn a commission at no extra cost to you. Nobody pays to be included. More on who writes this and how we pick.

Sources

A. O. Smith: Residential Electric Water Heater Installation Instructions and Use & Care Guide, March 2021 (part 100341465) (aosmithatlowes.com)
A. O. Smith: Residential Gas Water Heaters (direct vent) Installation and Operating Manual, 326940-001 (assets.aosmith.com)
A. O. Smith: Residential Gas Water Heater with FVIR, Installation Instructions and Use & Care Guide (100278381) (aosmithatlowes.com)
A. O. Smith: How to Drain & Flush a Water Heater (hotwater.com)
Rheem: Use & Care Manual, Residential Gas FVIR Certified Water Heaters (AP22543 Rev 04) (files.myrheem.com)
Rheem: Use & Care Manual, Electric Residential Water Heaters with Electronic Control (AP21980 Rev 02) (files.rheem.com)
Rheem: How Often To Flush Your Water Heater (And How To Do It) (rheem.com)
Bradford White: Installation and Operation Manual, gas-fired water heater with FVIR (238-51012-00V, rev. 08/26) (docs.bradfordwhite.com)
Bradford White: Installation and Operation Manual, electric water heater (238-55974-00C, rev. 08/26) (docs.bradfordwhite.com)
Bradford White For The Pro: Draining a Water Heater (forthepro.bradfordwhite.com)

How to Flush a Water Heater (Plumber’s Step-by-Step)