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How do you flush a water heater?

You can flush a tank water heater yourself unless the drain valve won't open or you're unsure about handling gas or electrical components, which is when Rheem says to consider professional help. Rheem advises flushing once a year, or every 6 months with hard water. Drain through a hose until the water runs clean, then refill before restoring heat.

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.
Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
Source: A.O. Smith, Instruction Manual, residential electric water heaters (ECT-40), read 24 October 2026.

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By InstaBids editorial team with AI research agents. Sources read: 24 October 2026 Updated 2026-10-24

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Key facts

How often should you flush a water heater?

Follow the manual for your own heater first, because the maker documents on this page give different intervals. Rheem's guidance for most households is once a year and every 6 months with hard water. One A.O. Smith gas manual recommends draining and flushing every 6 months, while its standard gas use and care guide recommends draining and flushing after the first six months to determine the amount of sediment build up, then annually if there is little sediment and more often if there is a lot. Bradford White's atmospheric gas manual lists a smaller monthly job: draining off a gallon to remove silt and sediment. Bradford White lists that monthly gallon as its own maintenance item, and Rheem's interval for hard water is the 6-month one.

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.
Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.
Source: Bradford White, Installation and Operation Instruction Manual, atmospheric vent gas water heater (238-54725-00), read 24 October 2026.

Rheem's article on how often to flush, read 24 October 2026: "For most households, it is recommended to flush your water heater once a year to help prevent sediment buildup and performance issues." and "If you have hard water, it’s recommended to flush your system every 6 months."

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.

A.O. Smith's manual for its direct-vent residential gas models, read the same day: "It is recommended that the tank be drained and flushed every 6 months to remove sediment which may build up during operation."

Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

Bradford White's atmospheric vent gas manual, read the same day, in its maintenance list: "Monthly drain off a gallon of water to remove silt and sediment."

Source: Bradford White, Installation and Operation Instruction Manual, atmospheric vent gas water heater (238-54725-00), read 24 October 2026.

How can you tell a water heater needs flushing?

Rheem lists rumbling or popping noises from the tank, rusty or cloudy hot water, running out of hot water faster than usual and longer recovery times between uses as signs it may be time to flush. A.O. Smith's gas use and care guide adds that heavy deposits can damage the water heater. Rheem explains the mechanism: sediment acts like insulation at the bottom of the tank, forcing the system to run longer heating cycles. Rheem says that if you see any of those signs, it is time to make flushing a priority.

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.
Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.

Rheem's article lists these signs, read 24 October 2026: "Rumbling or popping noises coming from the tank", "Rusty or cloudy hot water", "Running out of hot water faster than usual" and "Longer recovery times between uses".

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.

The same article says: "When sediment builds up, it acts like insulation at the bottom of the tank, forcing the system to run longer heating cycles".

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.

Is it better to drain a water heater or flush it?

A.O. Smith's direct-vent gas manual gives them as separate procedures. Its draining steps close the cold water inlet and open a nearby hot water faucet, left open to allow for draining. Its flushing steps keep the cold inlet open, with system water pressure applied to the water heater, and let the water flow until it runs clean. A.O. Smith's flushing steps start with making sure the cold inlet is open and end when the water runs clean. A.O. Smith's standard gas guide also warns that sediment can clog the drain valve itself, and says to contact a qualified person if you cannot get the tank to drain.

Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.

A.O. Smith's direct-vent gas manual, read 24 October 2026, in its flushing steps: "Flushing is performed with system water pressure applied to the water heater." and "Flush the water heater storage tank to remove sediment and allow the water to flow until it runs clean."

Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

A.O. Smith's use and care guide for a standard gas model, read the same day, says sediment "may clog the valve and prevent it from draining. If you can’t get the tank to drain, contact a qualified person."

Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.

Do tankless water heaters need flushing too?

Not in the same way. Rheem says tankless water heaters require periodic descaling instead of flushing, and its maintenance article recommends that the key tankless tasks be done at least once a year, often by a professional. Rheem also says a vinegar or descaling solution flush helps dissolve deposits. If your heater is a tank, the rest of this page applies; if it is tankless, follow the descaling section of its own manual.

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.
Source: Rheem, How to Keep Your Tank and Tankless Water Heaters Running at Peak Performance, read 24 October 2026.

Rheem's flushing article, read 24 October 2026: "Tankless water heaters, however, require periodic descaling instead of flushing."

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.

Rheem's tank and tankless maintenance article, read the same day: "Rheem recommends that these key maintenance tasks be performed at least once a year, often by a professional, to keep your unit in top shape." and "A vinegar or descaling solution flush helps dissolve deposits and keeps the unit running smoothly."

Source: Rheem, How to Keep Your Tank and Tankless Water Heaters Running at Peak Performance, read 24 October 2026.

Should you test the relief valve and anode when you flush?

The relief valve, yes: A.O. Smith's direct-vent gas manual and Bradford White's atmospheric vent gas manual each put that test at least once a year. The anode rod runs on a longer clock: Bradford White's gas manual says every 2 years, and A.O. Smith's electric manual says at a minimum every three years, by a qualified technician. Rheem's maintenance article describes the valve test as lifting the handle briefly so water flows through the discharge pipe. A.O. Smith says that if the valve does not reset and keeps releasing water, immediately close the cold water inlet and drain the water heater.

Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
Source: Bradford White, Installation and Operation Instruction Manual, atmospheric vent gas water heater (238-54725-00), read 24 October 2026.
Source: A.O. Smith, Instruction Manual, residential electric water heaters (ECT-40), read 24 October 2026.
Source: Rheem, How to Keep Your Tank and Tankless Water Heaters Running at Peak Performance, read 24 October 2026.

Bradford White's atmospheric vent gas manual, read 24 October 2026: "At least once a year, check the combination temperature and pressure relief valve to ensure that the valve has not become encrusted with lime." and "The anode rod should be inspected periodically (every 2 years) and replaced when necessary to prolong tank life."

Source: Bradford White, Installation and Operation Instruction Manual, atmospheric vent gas water heater (238-54725-00), read 24 October 2026.

A.O. Smith's direct-vent gas manual, read the same day: "If after manually operating the valve, it fails to completely reset and continues to release water, immediately close the cold water inlet to the water heater and drain the water heater".

Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

Does hard water mean you should flush more often?

Rheem says yes, and USGS gives the scale to measure it against. Rheem says to flush every 6 months with hard water, and USGS notes that when hard water is heated in a home water heater, solid calcium carbonate deposits can form. USGS also says its 1975 data are not designed for decisions on the scale of individual homeowner property, and that home-level hardness information should come from the local health agency or local water utility. The rows below pair the USGS bands with what that means for your flush schedule; the band comes from USGS, and the advice in each row is practical reasoning, not a USGS finding.

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.
Source: U.S. Geological Survey Water Science School, Hardness of Water, read 24 October 2026.

USGS Water Science School, read 24 October 2026: "0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard."

Source: U.S. Geological Survey Water Science School, Hardness of Water, read 24 October 2026.

Can you flush your own water heater, or hire a pro?

Rheem calls a flush manageable for many homeowners and recommends professional service for older units or heavy buildup. A.O. Smith's manuals name these risks: scalding from hot water, sediment that may clog the drain valve, and heat turned on before the tank is full. Plan the job for a time when nobody needs hot water, and keep the manual for your own model open next to you. This is practical reasoning, not legal advice and not a finding from any agency.

Source: Rheem, How Often To Flush Your Water Heater (And How To Do It), read 24 October 2026.
Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.
Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  1. Turn the heat off. A.O. Smith's gas manual says to turn the gas control knob to off and turn off the gas supply at the manual shut-off valve; its electric manual says to turn off the electric power supply before beginning.

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
    Source: A.O. Smith, Instruction Manual, residential electric water heaters (ECT-40), read 24 October 2026.

  2. Let the water cool. A.O. Smith's standard gas guide says: "Be sure the water runs cool before draining the tank to reduce the risk of scalding."

    Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.

  3. Close the cold inlet, open a hot faucet and connect the hose. A.O. Smith's direct-vent gas manual lists: "Close the cold water inlet valve to the water heater." "Open a nearby hot water faucet and leave open to allow for draining." "Connect a hose to the drain valve and terminate to an adequate drain."

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  4. Open the drain valve, as A.O. Smith's steps say, and watch how much grit comes out with the water.

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  5. Flush with pressure. A.O. Smith's flush steps begin: "Ensure the cold water inlet valve is open." With the drain still open, it says: "Flush the water heater storage tank to remove sediment and allow the water to flow until it runs clean."

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  6. Close the drain valve, remove the drain hose, and refill with a nearby hot water faucet open to allow air to escape, as A.O. Smith's refill steps list. It says to "keep the hot water faucet open for 3 minutes after a constant flow of water is obtained."

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  7. Make sure the tank is full before any heat goes on. A.O. Smith's gas manual: "Caution: Do not turn on the gas to the water heater unless the tank is full." Its electric manual: "Never use this water heater unless it is completely full of water."

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
    Source: A.O. Smith, Instruction Manual, residential electric water heaters (ECT-40), read 24 October 2026.

  8. Relight or restore power by the instructions on the label of your heater, as A.O. Smith's manual says, then look for drips at the drain valve and relief valve, the points Bradford White's refill steps name.

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
    Source: Bradford White, Installation and Operation Instruction Manual, atmospheric vent gas water heater (238-54725-00), read 24 October 2026.

Hire a pro when one of these applies. Bradford White's FAQ says it highly recommends a plumbing professional do the maintenance.

Source: Bradford White, What is the recommended maintenance for my water heater?, read 24 October 2026.

What to ask for in writing if you hire:

What should you have ready before you open the drain valve?

Have these in place before the first turn of the valve. A.O. Smith's standard gas guide warns that sediment may clog the valve and prevent it from draining, so a stuck valve is the point to stop and call a qualified person.

Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.

  1. Your heater's own manual, open to its draining section.
  2. A hose on the drain valve that runs to an adequate drain, as A.O. Smith's steps put it, and the area below it clear.

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  3. The water cooled first; A.O. Smith says: "Be sure the water runs cool before draining the tank to reduce the risk of scalding."

    Source: A.O. Smith, Use and Care Guide, residential atmospheric gas water heater (GCRL-30), read 24 October 2026.

  4. The gas control and gas supply off, or the electric power supply off, per the A.O. Smith steps above, and labelled so nobody turns it back on mid-job.

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.
    Source: A.O. Smith, Instruction Manual, residential electric water heaters (ECT-40), read 24 October 2026.

  5. A nearby hot water faucet open to allow for draining, and open again on the refill to allow air to escape (A.O. Smith's steps).

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  6. A plan for the refill; A.O. Smith says to "keep the hot water faucet open for 3 minutes after a constant flow of water is obtained."

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

  7. Your thermostat target; Bradford White warns: "Scalding may occur within five (5) seconds at a temperature setting of 140°F (60°C)."

    Source: Bradford White, Installation and Operation Instruction Manual, atmospheric vent gas water heater (238-54725-00), read 24 October 2026.

  8. The relief valve test on the same visit, at least once a year per A.O. Smith.

    Source: A.O. Smith, Installation and Operating Manual, residential direct-vent gas water heaters (328740-000), read 24 October 2026.

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Source: InstaBids process and privacy, live-page excerpts, read 24 October 2026.

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