Short answer
Rheem recommends flushing once a year, and every six months with hard water. Turn off the gas (set to pilot or off) or the breaker, shut the cold supply, open a hot tap, run a hose from the drain valve to a drain, and drain the tank. Then open the cold supply in bursts to stir up and flush sediment until the water runs clear. Refill completely, with a hot tap running steadily, before you turn the heat back on.
What you need
Steps
Turn off the heat
Gas: turn the gas control to “pilot” or “off” per your manual. Electric: switch off the breaker. Heating an empty electric tank burns out the elements.
Let it cool, or be careful
Water in the tank is hot enough to scald. Waiting a few hours, or running hot water first, makes the job safer.
Shut the cold supply
Close the valve on the cold water pipe going into the top of the tank.
Connect a hose
Screw a garden hose onto the drain valve near the bottom of the tank and run it to a floor drain, outside below the tank level, or a bucket.
Open a hot tap and the drain
Open a hot water tap upstairs to let air in, then open the drain valve. The tank drains in 10 to 30 minutes.
Stir up the sediment
With the drain open, open the cold supply for a few seconds at a time. The rush of water stirs the sediment and carries it out. Repeat until the water runs clear in a bucket.
Close and refill
Close the drain valve and remove the hose. Open the cold supply fully and leave the hot tap open until water flows steadily with no sputtering, so the tank is full.
Turn the heat back on
Gas: return the control to “on” or relight per the manual. Electric: switch the breaker back on only once the tank is full. Check the drain valve for drips.
Why flushing matters
Rheem explains that sediment forms as minerals separate and settle at the bottom of the tank, and recommends flushing yearly, or every six months with hard water (Rheem). On gas tanks the layer sits between the flame and the water; on electric tanks it can bury the lower element, which is a common reason elements fail. Popping or rumbling while heating is the sound of water trapped under sediment.
While the tank is drained
- Check the anode rod. It is the best time: how to check and replace it.
- Swap a plastic drain valve for a full port brass one if it clogged or dripped.
- Test the T&P valve once the tank is refilled and hot: relief valve guide.
Questions people ask
How often should I flush my water heater?
Rheem recommends once a year, and every six months if you have hard water.
What if the drain valve is clogged?
Sediment often blocks the drain valve. Close it, remove the hose, and gently poke the opening with a stiff wire, or open and close the cold supply to push water through. Some owners replace the stock valve with a full port brass valve that passes sediment more easily.
Is it bad to flush an old water heater that has never been flushed?
Sometimes a neglected tank’s plastic drain valve does not reseal, or sediment was covering a weak spot. Have a replacement drain valve on hand, and weigh it up if the tank is past about 10 years.
Should I flush a water heater with vinegar?
Some makers describe descaling for hard water. Follow your heater’s manual, and rinse thoroughly afterward.
Sources
Last reviewed October 29, 2026. Models, codes and listings change; check your heater’s manual and your local code, and follow the maker’s instructions.