Every water heater slowly fills with sediment. Calcium and rust settle out of the water and collect on the bottom of the tank, and on a gas heater they sit between the burner and the water it is trying to heat.
That costs money every month, slows recovery and shortens the life of the tank. Clearing it out takes an afternoon and a garden hose, most of it waiting. This walkthrough follows Word of Advice TV on a standard tank heater.
Flushing and draining are not the same job
Draining empties the tank and leaves it empty: the job when the heater is coming out, when it is leaking, or when a house is closed up for winter. Flushing clears sediment off the bottom of a heater that stays in service. You part-drain it, then pulse the cold supply back on in bursts so the incoming water lifts the grit and the hose carries it out.
The first half of each is the same, so the steps below cover both. Coming out for good? Drain it this way, then see how to install a water heater. If your unit is a wall-mounted box with no storage tank, none of this applies - a tankless heater is descaled by pumping vinegar through it.
What you need
A garden hose, a flathead screwdriver, a bucket, and somewhere below the level of the heater for the water to go. That is the list, though a spare brass drain valve and teflon tape are worth having on hand.
Gas and electric shut down in different orders
On gas the control dial goes to PILOT or VACATION, not OFF. Pilot stops the burner without putting the flame out, so there is nothing to relight afterwards.
On electric there is no dial, and this is the one that bites people. Switch the breaker off at the panel before any water leaves the tank. An element that fires with no water around it burns out in under a minute, and you find out when the hot water never comes back. Leave it off until the tank is full again.
Water leaving the hose is at tank temperature, 120 to 140°F, so keep children and pets clear. If the shut-off above the heater will not budge, the house main is the fallback: how to shut off water to your house covers where that valve hides and how to free a seized one.
How often, by water hardness
Manufacturers say once a year. In practice plenty of thirty-year-old tanks have never been flushed and are still running.
Hard water earns the annual flush - white scale on the kettle and crust round the shower head means that is you. Soft or softened water is fine every two or three years. Do not know the tank's history? Flush it once and read the answer off the hose: brown grit means make it yearly, clear water in two minutes means you can relax.
When the drain valve clogs or will not reseal
A valve that opens then slows to a dribble has a flake of scale across it. Shut it and open it again fast to blow the piece through, or work a straightened coat hanger into the port with the supply off. Never put pliers on a plastic valve.
A valve that drips after you close it has caught grit on the seat and will not clear itself. The tank is empty anyway, so unscrew it, tape the threads and fit a brass replacement. Ten minutes, a few dollars.
Refilling without an airlock
Air has to get out before water can get in, so the hot tap stays open while the tank fills. Sputtering there is the air leaving; a steady stream means it is full. The heat goes back on only then.
Draining for winter
A house left empty through a freeze needs the tank drained and the lines blown out, not the thermostat nudged down. Same procedure, all the way to empty, gas or breaker off until someone is back. Winterizing the sprinkler system fits the same afternoon, and how to thaw frozen pipes is better read before you need it.
