Flushing a tank water heater is meant to carry out some of the sediment that settles at the bottom. The idea is straightforward; the risk comes from working with a container full of hot water that is also connected to electricity or gas.
Sequence matters: shut down the energy source first, control the water second, and only then put the heater back in service.
Make sure you have a tank-style heater
This procedure is not for a tankless heater. Tankless units are usually descaled through a different service procedure. Find the manual for your exact model before starting.
Turn the heater off and let the water cool
Stored hot water can cause severe burns. Shut the heater down in advance and allow it to cool according to the manufacturer’s instructions. For an electric unit, turn off the correct circuit. For gas, use the shutdown procedure specified for the appliance.
Close the cold supply and prepare a safe drain path
Attach a suitable hose to the drain valve near the bottom of the tank. Route the other end to a drain or location that can safely handle the water without flooding the home or damaging landscaping.
Close the heater’s cold-water inlet and open a hot-water faucet in the house. The open faucet lets air enter while the tank drains.
Open the drain valve gently
Open it slowly. If little or no water comes out, do not beat on or force an old valve. Sediment can clog the outlet, and a brittle valve can break.
Rheem recommends professional help when a drain valve will not open, leaks, or the unit is old and heavily fouled. The goal is maintenance, not turning a stable old heater into an emergency leak.
Draining and flushing are not quite the same
Draining removes water. Flushing also tries to move loose sediment out. Some manufacturers instruct owners to briefly reopen the cold-water supply during the process to stir sediment and carry it out through the hose. Follow the procedure for your model rather than improvising.
Refill completely before restoring power
Close the drain valve, remove the hose, and reopen the cold-water inlet while leaving a hot faucet open. Air may sputter at first. Once the flow becomes steady, let it run briefly and then close the faucet.
Do not energize an electric tank until you know it is full. Heating elements can fail quickly if they are powered while exposed to air.
Check for leaks before you leave
Dry the drain valve and any fittings you handled, then watch them for several minutes. A valve that starts dripping after maintenance needs attention.
Many manufacturers use annual flushing as a general reference, although hard water, usage, and the model can change that schedule. A successful flush ends with a full tank, no leaks, and a normal restart—not with a rushed sequence.
Sources
- Rheem — How Often to Flush Your Water Heater — General guidance on draining, sediment, service intervals, and when to call a professional.
- CDC — Preventing Waterborne Germs at Home — Notes that many manufacturers recommend periodic flushing and advises following manufacturer instructions.