Yardtally is reader-supported. Some links on this page are affiliate links. As an Amazon Associate, Yardtally earns from qualifying purchases. See our Affiliate Disclosure.
Knowing how to flush a water heater is one of the easiest ways to make your tank last longer and run better. Minerals in your water settle to the bottom of the tank as sediment, and over time that layer makes the heater work harder, rumble, and wear out sooner. Flushing it takes about an hour, a garden hose, and no special skills.
This guide covers what sediment does to a water heater, the signs yours needs flushing, how often to do it, the 8 steps to flush a water heater safely, and what to do if something goes wrong.
WHAT’S IN THIS GUIDE
Why Flush a Water Heater?
Your water carries dissolved minerals like calcium and magnesium. When it’s heated in the tank, some of those minerals settle out and collect on the bottom as sediment. A. O. Smith, one of the largest water heater makers, says that buildup increases the risk of leaks, bad smells, and other common water heater problems, and it can lower efficiency and raise your energy bill. Source: A. O. Smith — How to Flush a Water Heater
University of Florida Extension explains why: sediment slows down the transfer of heat from the burner or elements into the water. The water heater has to run longer to heat the same amount of water, and the bottom of the tank takes more wear. Source: UF/IFAS Extension — Energy Efficient Homes: Water Heaters
Signs Your Water Heater Needs Flushing
Watch for these:
- Rumbling, popping, or crackling sounds from the tank while it heats. That’s water trapped under the sediment boiling and bursting through.
- Hot water runs out faster than it used to.
- Rusty, cloudy, or gritty hot water, or bits of sediment in faucet aerators.
- A rotten-egg smell from the hot water only.
- It’s been more than a year since the last flush, or you can’t remember ever doing it.
If you have hard water, and much of central Indiana does, sediment builds up faster. Crusty white scale on your faucets and showerheads is a good sign your water is hard.
How Often to Flush a Water Heater
A. O. Smith says most water heaters should be flushed at least once a year, and more often if you have hard water. Source: A. O. Smith — How to Flush a Water Heater
Between full flushes, University of Florida Extension recommends draining about a quart of water from the tank every 3 to 6 months to clear out loose sediment before it builds up. It’s a five-minute job: put a bucket under the drain valve, open it until about a quart runs out, and close it again. Source: UF/IFAS Extension — Energy Efficient Homes: Water Heaters
Fall is a good time for the yearly flush, before winter puts the heaviest load on your water heater. It’s one more task worth adding to our winter home maintenance checklist.
What You’ll Need
You probably have most of this already: A garden hose long enough to reach a floor drain, a sump, or outside
- Heavy work gloves and safety goggles since the water can be very hot
- A flashlight to see the valves and labels on the tank
- A bucket and a few old towels for drips
How to Flush a Water Heater in 8 Steps
These steps are for a standard tank water heater, gas or electric. Always check the manual for your model first, and if anything on the tank looks rusted, leaking, or different from what’s described here, stop and call a plumber.
Step 1: Turn off the gas or the power
For a gas water heater, turn the gas control knob to OFF and close the gas valve on the supply line. For an electric water heater, switch off its breaker at the main panel. A. O. Smith notes that turning the heater off first also lets the water cool, which reduces the risk of scalds. Source: A. O. Smith — How to Flush a Water Heater
Step 2: Let the water cool
Water straight out of the tank can be hot enough to burn. If you can, turn the heater off the night before and flush it in the morning. Either way, wear thick gloves and safety goggles while you work.
Step 3: Shut off the cold water supply
Find the cold water pipe going into the top of the water heater and close the shutoff valve on it. If your heater doesn’t have its own valve, use the main water shutoff for the house.
Step 4: Open a hot water faucet
Open the hot side of a sink faucet, ideally one upstairs or on the same floor. This lets air into the tank so the water can drain out instead of being held in by a vacuum.
Step 5: Connect a hose to the drain valve
The drain valve is near the bottom of the tank and looks like a small spigot. Screw a garden hose onto it and run the other end to a floor drain, a sump pit, or outside to a spot lower than the valve. Make sure the hose end won’t spray hot water on anything that could be damaged.
Step 6: Open the drain valve and flush until the water runs clear
Open the drain valve and let the tank drain. Once it’s mostly empty, briefly turn the cold water supply back on to stir up the sediment on the bottom and flush it out the hose. Keep flushing with cold water until the water coming out runs clear. Source: A. O. Smith — How to Flush a Water Heater
Step 7: Close the valve and refill the tank
Close the drain valve, remove the hose, and turn the cold water supply fully back on. Leave that hot faucet open. It will sputter air at first. When water flows from it in a full, steady stream, the tank is full. Let it run for about 3 minutes to push out any trapped air, then shut it off.
Step 8: Turn the gas or power back on
For an electric water heater, this order matters. A. O. Smith’s manual warns not to turn the power back on until the tank is completely full of water. If the power comes on with an empty tank, the upper heating element can burn out in seconds, which is called a dry fire. Once the hot faucet runs full stream, switch the breaker back on. Source: A. O. Smith — Electric Water Heater Manual
For a gas water heater, open the gas valve, relight the pilot if yours has one, and turn the control knob back to its normal setting, following the instructions on the label on the front of the tank. Give it about an hour to heat back up.
While you’re there, check the temperature setting. University of Florida Extension says 120°F is the best balance of efficiency and function for most homes. Source: UF/IFAS Extension — Energy Efficient Homes: Water Heaters
Troubleshooting
A few things can go wrong during a flush, and most are easy to fix:
- The water barely trickles out. Sediment may be clogging the drain valve. Close the valve, turn the cold water on for a few seconds to build pressure, then open the valve again to blast the clog loose.
- The drain valve drips after you close it. Older plastic drain valves often don’t seal well after they’ve been opened. Screw a garden hose cap onto it to stop the drip, and have the valve replaced with a brass one.
- No hot water after the flush. For electric heaters, check that the breaker is on, and if it is, the element may have dry-fired and need replacing. For gas heaters, make sure the gas valve is open and the pilot is lit.
- Lots of sediment and the water never runs clear. A tank with years of buildup may need a plumber to clear it, or it may be close to the end of its life.
When to Call a Plumber
Call a plumber if:
- The tank itself is leaking or has rust around the bottom
- You smell gas at any point. Leave the house and call your gas company from outside.
- The drain valve won’t open, or breaks when you try to turn it
- The water stays rusty after a full flush
- Your water heater is more than 10 years old. University of Florida Extension suggests starting to shop for a new one at that age, before it fails.
Source: UF/IFAS Extension — Energy Efficient Homes: Water Heaters
If you have a tankless water heater, the process is different. Those are descaled by circulating a cleaning solution through them, so follow the maker’s instructions for your model. And while you’re in the basement, take a few minutes to prevent frozen pipes and change the furnace filter.
Frequently Asked Questions About Flushing a Water Heater
How long does it take to flush a water heater?
About an hour for most tanks, not counting the time to let the water cool. Draining a 40- or 50-gallon tank takes the longest. Plan on another hour for the water to heat back up.
Can I flush my water heater without turning it off?
No. Always turn off the gas or the power first. With the power on, an electric water heater’s elements can burn out as the tank drains, and a gas burner can overheat an empty tank.
What happens if you never flush your water heater?
Sediment keeps building up on the bottom of the tank. Over time the water heater gets noisier, less efficient, and more expensive to run, and the buildup can contribute to leaks and a shorter life for the tank.
Why is my water heater making popping noises?
Popping or rumbling usually means sediment has built up on the bottom of the tank. Water trapped under the layer boils and bursts through it as the heater runs. Flushing the tank usually quiets it down.
Should I flush my water heater if I’ve never done it?
Usually yes, but go easy on an older tank. If the tank is many years old and has never been flushed, the drain valve may be stuck or may leak afterward. Have a hose cap and a replacement valve on hand, or call a plumber if the tank is near the 10-year mark.
What temperature should my water heater be set to?
120°F is the recommended setting for most homes. It’s hot enough for everyday use and helps keep energy costs down.