Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
Sediment settles at the bottom of a storage water heater over time, and it is the most common cause of a rumbling or popping noise from the tank. This page walks you through draining a storage-type water heater, electric or gas, to flush that sediment out through the drain valve. It also covers refilling the tank afterward so you do not restore power to an empty tank.
This page does not give lighting steps for a gas control: those steps differ by manufacturer and model and belong in your water heater's own manual. It also does not have you open the temperature and pressure relief valve to add air during the drain, because that valve can fail to close again; a hot water faucet elsewhere in the house does the same job more safely. If the drain valve will not close after the flush, this page tells you to call a plumber rather than force it.
Necessary equipment
| Item | Note |
|---|---|
| Garden hose | The hose must reach a floor drain or the outdoors. |
| Bucket optional | Use a bucket if no floor drain or outdoor drain is within reach of the hose. |
| Flashlight optional | The space around a water heater is often dark. |
| Flathead screwdriver optional | Some drain valves need this tool to open. |
| Pen and paper optional | Use these to record the date of the flush. |
Specifications
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
Before you start
Estimated 2 min to 7 min
KEEP YOUR SKIN AWAY FROM THE WATER FROM THE DRAIN VALVE.
The water in the tank can scald your skin.
- Isolate the water heater from its power supply.<1mReport a problem with step 1, Before you start
- Set the circuit breaker for an electric water heater to OFF.
- Read the rating plate on a gas water heater for its own shutdown steps.
- Close the cold water valve on the water heater.<1mReport a problem with step 2, Before you start
- This valve is usually on the pipe above the water heater.
- Turn the valve clockwise to close it.
- Find a garden hose for this task.1mReport a problem with step 3, Before you start
- The hose must reach a floor drain or the outdoors.
- Use a bucket if no floor drain or outdoor drain is within reach.
Drain the tank
Estimated 7 min to 25 min
- Attach the garden hose to the drain valve at the base of the water heater.1mReport a problem with step 1, Drain the tank
- The drain valve is near the bottom of the tank.
- Place the other end of the hose in the floor drain, outdoors, or the bucket.
DO NOT LIFT THE HANDLE ON THE RELIEF VALVE TO ADD AIR.
A relief valve that does not close again can send hot water into the room.
- Open a hot water faucet in the house.<1mReport a problem with step 2, Drain the tank
- Leave this faucet open until you finish the flush.
- This faucet lets air into the tank so it can drain.
- Open the drain valve to release water from the tank.<1mReport a problem with step 3, Drain the tank
- Use a flathead screwdriver if the valve has no handle.
- Direct the first water away from your skin.
- Let the tank drain until the water runs clear.5mReport a problem with step 4, Drain the tank
- Sediment leaves the tank in the water at the start of the drain.
- A full drain can take several minutes.
Refill the tank
Estimated 4 min to 7 min
CALL A PLUMBER IF THE DRAIN VALVE DOES NOT CLOSE FULLY.
A forced valve can break and cause a leak.
- Close the drain valve when the water runs clear.<1mReport a problem with step 1, Refill the tank
- Remove the garden hose from the drain valve.<1mReport a problem with step 2, Refill the tank
- Open the cold water valve on the water heater.<1mReport a problem with step 3, Refill the tank
- A steady flow from the faucet shows a full tank.
- Let the hot water faucet run until the flow is steady.3mReport a problem with step 4, Refill the tank
- This clears trapped air from the tank and the pipes.
- This step can take a few minutes.
- Close the hot water faucet.<1mReport a problem with step 5, Refill the tank
After the flush
Estimated 2 min to 8 min
DO NOT TURN ON THE POWER SUPPLY UNTIL THE TANK IS FULL OF WATER.
An empty heating element can fail or overheat.
- Restore power to the water heater.<1mReport a problem with step 1, After the flush
- Set the circuit breaker for an electric water heater to ON.
- Follow the manual for a gas water heater to restore normal operation.
- Examine the drain valve for a leak after the flush.1mReport a problem with step 2, After the flush
- A dry valve shows a good seal.
- Write the date of this flush in your records.<1mReport a problem with step 3, After the flush
- This date sets your next flush interval.
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- water heater
- Also called: hot water heater, hot water tank, hot water cylinder, boiler, geyser
- sediment
- Also called: scale, mineral buildup, tank scale, sludge
- drain valve
- Also called: spigot, boiler drain, hose bib, tank drain
- relief valve
- Also called: T&P valve, TPR valve, pressure relief valve, temperature and pressure relief valve, pop-off valve
When to use a professional
Call a plumber if the drain valve leaks or does not close after the flush. Do not force a valve that will not close.
Read the manual for a gas water heater before you restore its normal operation. This page gives no lighting steps for a gas control.
Call a qualified service technician for a wiring fault, a thermostat fault, or a heating element fault. Do not repair these parts yourself.
Call a plumber if you cannot find the cold water valve or the drain valve. Call a plumber also if sediment returns within a few months of a flush.
Common questions
Why does my hot water heater make a rumbling or popping noise?
Sediment is the usual cause. Rheem's own troubleshooting table for a rumbling noise names the cause as 'water conditions in your home caused a build up of scale or mineral deposits in the water heater' and gives the fix as 'allow a few quarts of water to run from drain valve to remove sediment settlings.' The sediment settles at the bottom of the tank and is disturbed when the heating element or burner runs, which is what produces the noise. A full flush, the task this page covers, clears more of it than a quick partial drain does.
How often should I flush a water heater?
Sources disagree, and this page does not pick a winner. Rheem's own consumer article and one AO Smith page say roughly once a year, twice a year with hard water. A second AO Smith page gives that same interval for professional servicing as a whole rather than for flushing on its own. Rheem's own use and care manual says something different: a few quarts drained every month. Those are not quite the same action, a brief monthly partial drain against a full annual flush, and none of the four documents mentions the other. Use the interval and the method printed in the manual for your own water heater.
Can I open the pressure relief valve to let air into the tank while I drain it?
This page does not have you do that, even though at least one manufacturer manual lists it as an option alongside a hot water faucet. A relief valve is a safety device, and this site already carries a separate warning, grounded in a manufacturer DANGER notice, that this valve can fail to close again once it is operated. A hot water faucet elsewhere in the house lets air into the tank the same way without touching that valve. See the related page on inspecting a water heater's relief valve discharge pipe for more on that valve.
Do I need to turn off the gas to flush a gas water heater?
Yes, but this page does not walk you through how. Manufacturer instructions on this point are 'turn off the gas' in general terms, and the exact position of the gas control and how to restore it afterward vary by model and by ignition type. Read the rating plate on your water heater or its manual for the exact steps, both to shut it down before the flush and to restore it afterward. This page limits itself to the parts of the task that do not touch a gas control.
What if the drain valve on my water heater will not close after I flush it?
Stop and call a plumber. A worn or corroded drain valve can jam partly open, and forcing it can break the valve body and turn a slow drip into a flood. This page treats a valve that will not close as a professional-referral point, not as a step to push through. Keep a bucket under the valve and shut the cold water valve again if the drain valve keeps leaking while you wait for a plumber.
Is flushing a storage water heater the same as descaling a tankless one?
No. Rheem draws this line itself: 'Tankless water heaters, however, require periodic descaling instead of flushing.' A storage water heater holds standing water and settles sediment at the bottom of the tank, which this page's drain-valve method removes. A tankless water heater heats water as it passes through a heat exchanger and instead accumulates mineral scale on that exchanger, which needs a circulated descaling solution. See the related page on descaling a tankless water heater if that is your equipment.
Related procedures
- How to find and record the model and serial number of every appliance in the house
- Where is the water under my hot water heater coming from, and does it mean I need a new one?
- How do I check if my water heater's pressure relief valve pipe is installed correctly
- How to descale or flush a tankless water heater, and whether vinegar or a CLR-type descaler is safe to use
- How hot should my hot water be and how do I check it
- How do I read the label on my hot water heater and figure out what the numbers mean
- How old is my water heater and how do I read the serial number
- How to fix a toilet tank that fills too high or too low, and set the correct water level at the fill valve
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1How to Flush a Water Heater
- Tier 1Water Heater Maintenance Checklist
- Tier 1How Often To Flush Your Water Heater (And How To Do It)
- Tier 1Electric Residential Hybrid Water Heater Use & Care Manual (AP23657 Rev 04)
- Tier 1Avoiding Tap Water Scalds (CPSC Publication 5098)
Revision history
Current version 2 · updated 2026-08-04 · next review due 2027-08-04
- v2 · 2026-08-04The AO Smith maintenance checklist was counted as a fourth source for a FLUSHING interval. It gives 'once a year. Twice a year, if you have hard water.' as the answer to 'How often should I schedule professional water heater maintenance?' — professional servicing as a whole. The figure is unchanged and the page still refuses to average the four documents; what changed is that the checklist is now described as answering the question it actually answers.
- v1 · 2026-08-04First draft. Draining a storage-type (tank) water heater, electric or gas, to remove sediment through the drain valve, and refilling it afterward. Primary sources: AO Smith's own hotwater.com 'How to Flush a Water Heater' page (staged this session as hotwater-how-to-drain-a-water-heater) for the full step sequence, and Rheem's already-registered rheem-hpwh-use-care-manual (AP23657 Rev 04), page 29, read directly by downloading the PDF and running it through scripts/lib/pdftext.py: 'CAUTION: Shut off power to the water heater before draining water.' / 'In order to drain the water heater, turn off the cold water supply. Open a hot water faucet or lift the handle on the relief valve to admit air to the tank.' / 'Attach a garden hose to the drain valve on the water heater and direct the stream of water to a drain. Open the valve.' Page 15 of the same manual, quoted: 'WARNING: DO NOT turn on the electrical supply or operate this water heater unless it is completely full of water. The tank must be full of water before water heater is turned on. The water heater warranty does not cover damage or failure resulting from operation with an empty or partially empty tank.' and, on refilling: 'Make certain the drain valve on the water heater is completely closed. Open the shut-off valve in the cold water supply line. Open each hot water faucet slowly to allow the air to vent from the water heater and piping. A steady flow of water from the hot water faucet(s) indicates a full water heater.' Page 31 troubleshooting table, quoted for the FAQ on rumbling noise: cause 'water conditions in your home caused a build up of scale or mineral deposits in the water heater', fix 'allow a few quarts of water to run from drain valve to remove sediment settlings.' Page 29 also carries a DANGER notice on manually operating the relief valve ('the water drained from the tank may be hot enough to present a scald hazard') and, separately, a monthly partial-drain figure that disagrees with Rheem's own consumer article on flush frequency; both are published as-is rather than reconciled, per the record's specification conflict_note. This record deliberately does not instruct lifting the relief valve to admit air, even though the manual lists it as an option alongside a hot water faucet, because this site already carries a WARNING (on inspect-a-water-heater-relief-valve-discharge-pipe, grounded in a Rheem DANGER notice) that this valve can fail to reseat once operated; the hot-water-faucet method is used instead. This record also deliberately does not describe operating a gas control of any kind, per the backlog note for this topic: gas shutdown and restart are routed to the water heater's own rating plate and manual. cpsc-tap-water-scalds-5098 is cited for the general scald hazard supporting the page-opening WARNING. Two new AO Smith sources were staged: hotwater-how-to-drain-a-water-heater and hotwater-water-heater-maintenance-checklist (the latter corroborating the hard-water flush interval only). No specification in the safety_critical_specs sense (torque, pressure, voltage, temperature limit) applies to this task; the one specification entry records the flush-interval conflict rather than a safety-critical numeric value.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.