Short answer
To flush a water heater, follow your manufacturer's instructions first. Turn off the power or gas, let the hot water cool or replace it with cold, close the cold supply, drain the tank through the drain valve, then flush and refill. Hot water burns and an old stuck valve can leak, so hire a plumber if you doubt any step. Sources disagree on how often.
Sediment collects at the bottom of a tank water heater, and a water heater flush is the routine way to remove it. Draining the tank is part of it. This page explains why sediment matters, what the manufacturer decides, the safety rules, the general steps public agencies publish, and what the sources say about how often to flush. It also covers the signs that mean you should not try it yourself. It is written for tank-type storage heaters, gas or electric.
Water heater sediment: why it matters
Water carries minerals, and they settle in the tank. City and state sources give several reasons to remove them.
- Efficiency and clogs. The city of Blaine, Minnesota says sediment buildup can reduce a water heater's energy efficiency and clog water lines, and that flushing can increase the life of the unit.
- Heating and capacity. ENERGY STAR says that as tanks age, sediment can build up and reduce capacity. It lists reduced hot water supply from sediment and rumbling noises from sediment on the tank bottom among the signs of a failing heater.
- Health. The New Jersey Department of Health says sediment buildup around the heating element makes the heater work harder and can promote the growth of waterborne bacteria, including the kind that cause Legionnaires' disease.
- Hard water. A. O. Smith's consumer guide says hard water causes faster sediment buildup, so heaters in mineral-heavy areas need flushing more often.
If your heater is rumbling, popping or not keeping up, see water heater not heating before you assume sediment is the only cause.
The manufacturer's instructions come first
Every source here says the same thing. The city of Rockford, Illinois says to always follow the procedure in your water heater manufacturer's manual and to use its own steps only if the manual is not available. The New Jersey Department of Health says you must refer to the original manufacturer's instructions and tells you to read the owner's manual and the instructions posted on the side of the tank. The US Department of Energy says to read your owner's manual for specific maintenance recommendations.
Heaters differ in drain valve type, gas control and how they should be shut down and restarted. Find the manual, or search the model number from the tank label on the manufacturer's site. If you cannot find instructions for your model, call a plumber instead of improvising.
Safety before you touch anything
- Power or gas off first. The New Jersey Department of Health says to shut off the electrical power or the gas before draining, or you could damage the heating components. For electric heaters it says to use the labelled breaker or fuse. For gas heaters, check the manual to see whether to shut the manual gas valve or switch the gas control to off or pilot mode.
- Hot water burns. The same source says the water can be very hot and suggests protective goggles and heavy-duty rubber gloves. It says to either run the hot taps to replace the tank's hot water with cold or let the water cool, typically overnight. Blaine tells you to put the hose end where scalding water will not do harm.
- Do not touch the pressure relief valve while the heater is hot. A. O. Smith warns that scalding water can shoot out. Some city guides open it as part of the process and others do not, so follow your manual.
- Keep children and pets clear of the work area.
- Who should not do it. New Jersey says people at increased risk, such as people aged 50 and over, smokers, people with weakened immune systems and chronic lung disease, should not take part in draining and flushing because of aerosolized water that may carry bacteria.
- If you smell gas at any point, leave and call the gas utility from outside. Do not relight a pilot unless the label on your heater describes how, and follow the label exactly.
How to flush a water heater: general steps
These steps combine what the New Jersey Department of Health, Blaine, Minnesota and Rockford, Illinois publish. They are general. Where they differ from your manual, your manual wins.
- Read the manual and the tank label. Gather a garden hose, a bucket, towels, and a hose cap or screwdriver if the manual calls for them.
- Turn off the electricity at the breaker, or shut off the gas as the manual directs.
- Let the hot water cool or replace it. Run hot taps to bring in cold water, or wait, as above.
- Open a hot tap on an upper floor. New Jersey says this releases pressure and keeps a vacuum from forming that would stop the tank draining.
- Close the cold water supply valve on the pipe above the heater.
- Attach the hose to the drain valve and run it to a floor drain, a sink, a bucket or outdoors. New Jersey says the hose should be lower than the drain valve.
- Open the drain valve and let the tank empty. If you use a bucket, close the valve while you empty it.
- Flush. New Jersey and Rockford both describe briefly turning the cold supply on to stir up sediment, then draining again until the water runs clear.
- Close the drain valve fully and remove the hose. Check that it is not leaking.
- Refill. Open the cold supply with the hot tap still open, and close the tap once water flows steadily. Rockford says to open hot and cold taps in the house to expel trapped air.
- Only when the tank is full, restore the power or gas as the manual directs. New Jersey says you should have hot water within an hour or so.
If the pilot light went out during the job, relight it only by following the label on the heater and only if you smell no gas. If it will not stay lit, call a professional.
How often to flush a water heater
The sources do not agree, so here they are side by side. This is a point where your manual and your water quality should decide.
| Source | What it says |
|---|---|
| US Department of Energy (Energy Saver) | Routine maintenance may include flushing a quart of water from the tank every three months, depending on the model, plus checking the pressure relief valve every six months and inspecting the anode rod every three to four years. |
| City of Blaine, Minnesota | Flush every one to three years depending on the model and water source. |
| City of Rockford, Illinois | At least once a year, maybe more often depending on where you live. |
| A. O. Smith consumer guide | Drain a few gallons from the tank once a year, and more often in areas with hard water. |
Note that the Department of Energy figure describes drawing a quart from the tank, a smaller job than a full drain. The range runs from every few months to every few years. If you do not know when the tank was last flushed, treat it as a first flush and read the next section.
When not to attempt it yourself
- The heater has never been flushed or has not been for years. The New Jersey Department of Health says that if it has not been drained recently, the valves can rust and become hard to close completely once opened, which can lead to leaking and water damage. A drain valve that will not close is a plumber's job.
- The tank is old, rusted or leaking. ENERGY STAR lists corrosion on or around the unit, leaks at joints or seams and rust in the water as signs of possible failure, and says to consider replacing a heater more than 10 years old. See how long does a water heater last. Do not force an old drain valve.
- You have anode rod questions. The anode rod is the sacrificial part that corrodes to protect the tank. The Department of Energy says to inspect it every three to four years, while A. O. Smith advises having a plumber check it once a year. Natural Resources Canada notes that it dissolves at a rate that depends on the water's mineral content or hardness. Natural Resources Canada says the rod is inserted into the tank from the top, so checking or replacing it means working at the top of the tank, which is a plumber's job unless your manual describes it.
- Anyone in the higher-risk groups above should not take part, per New Jersey.
- You cannot find instructions for your model, cannot reach the drain valve safely, or smell gas.
When to hire a professional
New Jersey's health department strongly recommends hiring a licensed or qualified plumber to drain and flush a water heater. In its 2025 document it gives $75 to $250 as an average cost, and says the actual cost varies with the type of heater and other issues. Treat that as one state's published figure and ask local companies for written quotes. A plumber can also check the pressure relief valve and anode rod.
The Department of Energy's advice for choosing a contractor applies here too: ask for cost estimates in writing, ask for references, and ask whether the company will obtain a local permit if one is needed. For more on vetting, see drain cleaning near me.
After the flush
Cloudy water or air in the taps can follow a flush. Let them run until the water clears. If rumbling continues or the tank leaks, call a plumber. On temperature, the Consumer Product Safety Commission urges 120 degrees Fahrenheit to reduce tap-water scalds. New Jersey calls 120 a minimum, says a higher setting may help control bacteria if you take extra care against scalding, and suggests a mixing valve where young children live. Natural Resources Canada cautions that setting it too low may promote bacterial growth. Ask a plumber about the right setting for your household.
What to look up where you live
- Your local building department: permits for water heater work are set locally. A flush is maintenance, but if the job grows into a new drain valve or a replacement heater, ask the local building department what is required.
- Your water utility or city public works: some publish guidance, like the cities quoted above.
- Your state or provincial plumbing licensing board: to confirm a plumber's licence.
For Canadian readers. Provinces and territories regulate plumbing, and municipalities run permits. Natural Resources Canada publishes a residential water heater guide. Costs are in Canadian dollars and are not comparable to US figures.
For plumbing company owners
Homeowners search for water heater service all year, and most are looking for a company they can trust to come to the house. If you want to be found when they search, read plumbing marketing plan and near me searches for plumbers and septic companies. You can also book a call with LiveLeadsLane. LiveLeadsLane is a marketing practice for contractors, not a directory, and it does not take jobs or refer homeowners.
