Water Heater Sediment: Get It Out and Keep It Out

By Ray Bennett · Updated 2 October 2026 · 7 min read · Checked against the maker’s manual

Water Heater Sediment: Get It Out and Keep It Out

Short answer

Catch the first bucket out of the drain hose and look at what settles in it. Clear means there is little to worry about, grit means an ordinary flush, and white flakes mean years of build up that a flush alone will not shift. On gas the crust wastes fuel, on electric it buries the lower element and burns it out early.

Water heater sediment is the white grit that hard water leaves behind every time it is heated. It sinks, it hardens on the bottom of the tank, and it quietly costs you money for years before it ever makes a noise.

Getting it out is an hour with a hose. The useful part is knowing how much you have first, because that decides whether a flush will do it.

Before you start

What to carry: a garden hose, a bucket, a flathead screwdriver and gloves. About an hour, and most of that is standing and waiting.

Gas or electric? The build up is the same but the damage is different. On a gas heater the burner is underneath, so the crust sits between the flame and the water. On an electric one there is no flame, and the problem is that the lower element ends up buried in the grit.

How old is the heater? Under about eight years, flush it without a second thought. Past twelve, read the warning below before you touch the drain valve.

Two things that turn a flush into a bad day. Refill it completely before the power goes back on. An electric element switched on in a tank that is not full burns out in seconds. Close the drain, open the cold inlet, and leave a hot tap upstairs running until the water comes out steadily with no spitting. Only then the breaker.

An old tank that has never been flushed is a judgement call. Scale can be sitting over a thin patch of steel and holding it, and stirring it up is sometimes what starts a leak. Past about twelve years, if it is working, many people leave it alone and put the money towards the next heater instead.

How much have you actually got?

Catch the first bucket, let it stand for a minute and look at the bottom. What settles tells you which job you are doing.

Check 1

Do the bucket test before you flush anything

Put the hose on the drain valve, run a bucket, shut it off again and let it stand for a minute.

Water that runs clear means there is very little in there. Cloudy water with grit at the bottom is ordinary build up and a flush will handle it. White flakes and hard chunks mean years of it, and you should expect a deliming as well as a flush.

Two other signs count. A heater that rumbles and pops while it heats is boiling water trapped under a crust: what each noise means. And an electric heater that gives less hot water than it used to has often lost its lower element to the same grit.

What it is costing you

The same crust on the bottom of the tank does two different kinds of damage depending on how the water is heated.

On a gas heater the flame has to push its heat through the layer before it reaches any water. The burner runs longer for the same shower, and the bottom of the tank gets hotter than it should, which is what eventually pops and bangs.

On an electric heater the lower element sits down in the grit. It cannot get rid of its heat into the water, so it runs hot and fails years earlier than it should. That is the fault that shows up as hot water running out faster than it used to: how to test a water heater element.

Either way the tank itself works harder, and Whirlpool says sediment build up can make the tank fail early.

Flushing it out

Check 2Free, an hour

Drain it, then stir it with the cold inlet

Power or gas off first. On gas, Rheem says to shut the gas off at the gas control, so turn the dial to OFF. On electric, switch the breaker off.

Close the cold water valve going into the top of the tank. Put the hose on the drain valve and run it outside or into a bucket, and open a hot tap somewhere upstairs so air can get in behind the water.

When it is empty, open the cold inlet in short bursts. That is the part that matters. The rush of water lifts the grit off the bottom and carries it out of the hose, and simply emptying a tank quietly and refilling it does almost nothing.

Keep going in bursts until what comes out of the hose runs clear. Then close the drain, refill completely, and only then the power, or on gas relight the pilot.

When a flush will not shift it

Check 3

Deliming, for a tank that has gone years without one

A layer that has been baked on for years has gone hard, and water will not lift it however many bursts you give it.

Drain the tank, close the drain valve and put a few gallons of white vinegar or a proper descaling solution in through the hot water outlet or the anode rod opening on top. Leave it overnight, then drain it and flush again with the bursts.

Vinegar is slow and cheap, a commercial descaler is faster and stronger. Either way this is a bigger job than a flush, because something has to come off the top of the tank to get the liquid in.

If it still rumbles after that, the crust has bonded to the steel and it is noise rather than danger. On an older heater that is the point to stop spending on it.

The drain valve that will not drain

Check 4

Nothing comes out, or it stops halfway

First check the hot tap upstairs is actually open, because a sealed tank holds its water.

If it is open and nothing moves, the plastic drain valve is blocked with the very grit you are trying to remove. Poke it through with a flathead screwdriver or a straightened coat hanger, with the bucket ready, because it usually lets go all at once.

A tank that does this every time is worth a three quarter inch brass full port ball valve in place of the plastic one. It costs little, it clogs far less, and it drains much faster.

Keeping it from coming back

Flush it regularly. Whirlpool says to drain and flush the tank every six months, and Rheem suggests draining a few quarts every month. A heater flushed from new hardly ever builds a crust at all.

Turn it down to 120. Hotter water drops more scale out, so a tank sitting at 140 builds up faster as well as costing more to run and risking scalds.

A softener is the real answer in hard water. It is not cheap, but it stops the problem at the source and it saves the kettle, the dishwasher and the shower head at the same time.

Check the anode rod while you are in there. That rod is not about sediment, it protects the steel from rusting, but it is the other thing that decides how long the tank lives and the only time anyone looks at it is during a flush. A rod eaten down to the wire means the tank is next in line.

Questions people ask

How much sediment is normal?

Some grit in the first bucket is normal anywhere. Flakes you could pick up between your fingers are not, and mean it has gone a long time without a flush.

Can sediment make the water look cloudy at the tap?

It can, and so can air. Fill a glass and let it stand. Air clears from the bottom up in a few seconds. Grit settles to the bottom and stays there.

Is a tankless heater immune to this?

No. It has no tank to collect grit, but scale builds inside the heat exchanger instead and it needs descaling on a schedule rather than when it complains.

My water is soft. Do I still need to flush?

Less often, but yes. Softened water still carries some mineral, and the flush also tells you the drain valve still works, which matters on the day you actually need it.

Will flushing fix no hot water?

Not on its own. If there is no hot water at all, work through it in order first: the checks for a heater that is not working.

The water came out rusty, not white.

That is not sediment, that is the tank itself or the pipes. Brown water from the hot side only, on an older heater, usually means the anode is gone and the steel is rusting.

Sources: Whirlpool Energy Smart use and care guide 318686-001 (sediment noise and early tank failure, draining and flushing, elements covered with sediment), Rheem use and care manual AP23698 (draining, rumbling, anode rod) and the DOE Building America "Strategy Guideline: Proper Water Heater Selection" (2015) (hotter settings speed up sediment)