A tank water heater should be flushed at least once a year, and many experts say every six months. Flushing drains out the sediment that settles at the bottom of the tank. When it's skipped, the heater works harder, wears out sooner and is far more likely to leak.
Seven years ago we moved into the first house I'd ever owned. I'd never been responsible for a water heater before. After a while ours stopped keeping up, even though it was a 70-gallon tank. So I started reading. I assumed draining it would be hard, and I'd never done it. When I finally did, so much sediment came out. Afterwards it worked so much better.
Most people never think about the water heater until something goes wrong. It sits in a corner of the basement and does its job quietly for years. That's exactly why the flush gets forgotten.
What is the sediment in a water heater?
Water heater sediment is minerals from your tap water, mostly calcium and magnesium, plus small flakes of rust and grit. When water is heated, some of those minerals come out of the water and sink. Every day the heater runs, a little more settles on the floor of the tank.
The sediment never leaves on its own. Hot water is drawn off the top of the tank, so whatever sinks to the bottom stays there and keeps building.
Harder water makes more of it. If you don't know how hard your water is, a plumber can tell you.
What happens if you never flush a water heater?
A water heater that's never flushed costs more to run, wears out early and becomes more likely to leak. Here's what the sediment does over the years:
- It gets between the heat and the water. On a gas water heater the burner sits under the tank. A thick layer of sediment works like a blanket between the flame and the water, so the burner runs longer and the steel at the bottom of the tank runs hotter.
- It makes noise. A popping or rumbling sound when the heater fires usually means water is trapped under the sediment and boiling its way through.
- On an electric heater, it can bury the lower heating element, which then struggles and can burn out.
- It wears the tank out. A.O. Smith, one of the largest water heater makers, says skipped flushing lets sediment damage internal parts and shortens the heater's life.
- It clogs the drain valve. The longer a tank goes without a flush, the more likely the small valve at the bottom is to clog with sediment. So the job doesn't get easier by waiting. It gets harder.
How often should a water heater be flushed?
A tank water heater should be flushed at least once a year. Every six months is better, and hard water makes it more urgent.
- A.O. Smith, the manufacturer, says at least once a year, and more often with hard water.
- The Insurance Institute for Business & Home Safety recommends every six months.
- Your heater's owner's manual has the final word for your exact model.
One habit that helps: write the date of each flush on a strip of masking tape on the side of the tank. Then anyone who looks at the heater, including the next owner of the house, knows where things stand.
Does flushing a water heater make it last longer?
Yes. Regular flushing is one of the few things that directly helps a water heater last. A.O. Smith says flushing prolongs a unit's life and improves its efficiency, and that skipping it reduces its lifespan.
The other half of the job is the anode rod. It's a metal rod inside the tank that's designed to corrode so the tank itself doesn't. Once the rod is used up, the tank starts rusting from the inside. The Insurance Institute for Business & Home Safety recommends a plumber inspect the anode rod at least every two years, and every year once the warranty has run out.
Flushing and the anode rod together are the difference between a water heater that reaches old age and one that quits early. The dryer vent is another job that's easy to forget, and cleaning a dryer vent is a similar once-a-year habit.
How dangerous is a failing water heater?
The real danger is water, and a lot of it. A water heater usually fails in one of two ways: a slow leak from the bottom of a rusted tank, or a sudden burst. Either way, the tank keeps refilling from your water supply until someone shuts it off.
The timing matters too. Research from the Insurance Institute for Business & Home Safety found that the chance of a leak or burst starts climbing sharply once a water heater is five years old, and that three out of four water heaters fail before they turn twelve.
In many older homes in Summit, Chatham and Short Hills, the basement has been finished, so the water heater sits a few feet from carpet, drywall and storage. And if the family is in Florida for the winter or at the Shore for the summer, a slow leak can run for days before anyone walks downstairs. That's a big part of why someone should check on a house while you're away. If you're leaving for the winter, our guide to winterizing your house covers the heat setting, the outdoor faucets and the leak sensors worth having.
Honestly, this is the part that should get your attention. A flush is routine. A burst tank in a finished basement is not.
What can you check on your water heater this week?
You can learn a lot about your water heater in five minutes without touching anything:
- Find its age. Look for the label on the side of the tank. The manufacture date is usually built into the serial number, and the maker's website or customer line can decode it.
- Listen. Popping or rumbling when it heats up is the classic sound of sediment.
- Look at the base. Rust, dampness, a white crust or water in the pan underneath are all signs to call a plumber.
- Find the cold water shut-off valve. It's on the pipe going into the top of the tank. Knowing where it is means you can stop the water quickly if the tank ever leaks.
- Ask when it was last flushed. If nobody in the house knows, assume it's never been done.
When to call a professional
Flushing a water heater isn't hard once you know your heater, but it's not a job to learn by trial and error. It means turning down a gas control or switching off a heavy electrical circuit, handling near-boiling water, and opening a drain valve that may clog or refuse to close again on a tank that's gone years without a flush. A.O. Smith's own advice is to call a plumber if sediment stops the tank from draining.
If your heater is older and has never been flushed, ask the plumber whether a flush still makes sense or whether it's time to plan a replacement.
Call a plumber promptly if you see any of these:
- Water around the base of the tank or in the pan underneath
- Rusty or muddy hot water
- Water dripping from the pipe on the side of the tank (that's the relief valve)
- Hot water running out much sooner than it used to
- Loud, repeated popping or banging
If you ever smell gas near the water heater, leave the house and call the gas utility or 911 from outside.
On our regular home maintenance visits, the water heater gets a look every time, and the date of its last flush goes in the home's record.
Frequently asked questions
Do tankless water heaters need flushing?
Tankless water heaters don't have a tank, so there's nothing to drain. Many still need descaling with a cleaning solution and a pump kit to clear minerals from inside the unit. Check the manual for your model, and have a plumber do it if you're not sure.
Is it too late to flush an old water heater?
Not always, but it's a plumber's call. On a tank that's gone many years without a flush, the drain valve may clog or the sediment may be hiding a weak spot in the tank. A plumber can tell you whether flushing still makes sense or whether the money is better spent on a replacement.
How long does a water heater last?
Most tank water heaters don't make it far past ten years. Research from the Insurance Institute for Business & Home Safety found that three out of four fail before they turn twelve, and the risk of a leak rises sharply after year five. Regular flushing and anode rod checks help a heater reach the far end of that range.
Why is my water heater making a popping noise?
A popping or rumbling water heater usually has sediment at the bottom of the tank, with water trapped underneath it boiling through. Noises can have other causes too, so it's worth having a plumber look rather than guessing. Either way, a noisy water heater is telling you it's overdue for attention.
Does a water softener mean less sediment in a water heater?
Mostly, yes. A whole-house water softener removes the calcium and magnesium that make up most water heater sediment, so much less builds up in the tank. It doesn't catch everything, though: sand, grit and rust still settle at the bottom, so keep flushing on the schedule in your manual. Softened water also uses up the anode rod faster, and one water heater maker's manual says the anode needs checking more often in homes with a softener.
If you'd rather someone else kept track of this, that's what we do.
The Home Steward is a home management service based in Summit, New Jersey, run by Sebastian and Kory, caring for homes in Summit, Chatham, Short Hills and Millburn.
