Flushing a water heater once a year helps remove sediment and mineral buildup so the heater works more efficiently, heats water faster, and lasts longer.
In This Article:
Quick Answer
Why Water Heaters Need Flushing
How to Flush or Drain a Water Heater
Water Heater Won’t Drain
How to Back-Flush a Water Heater
How to Replace a Drain Valve
FAQs
Over time, minerals naturally found in water settle to the bottom of a water heater tank.
This sediment can form a thick layer of:
- Mineral scale
- Rust particles
- Calcium deposits
- Sediment sludge
In gas water heaters, the sediment forms above the burner area and reduces heat transfer into the water.
In electric water heaters, sediment can accumulate around the lower heating element.
This buildup can:
- Reduce heating efficiency
- Increase energy costs
- Cause popping or rumbling sounds
- Slow hot water recovery
- Shorten tank life
- Clog the drain valve
Regular flushing helps remove these deposits before they become severe.
Quick Answer
To flush a water heater, turn off power or gas, close the cold-water supply valve, connect a garden hose to the drain valve, open a hot-water faucet, and flush several gallons from the tank until the water runs clear.
Don’s Advice
If a water heater has never been flushed and is already very old, some plumbers recommend leaving it alone unless problems already exist.
The concern is that heavy sediment buildup may actually be helping seal tiny internal corrosion holes that could begin leaking once the sediment is removed.
Why Water Heaters Need Flushing
Water naturally contains dissolved minerals such as calcium and magnesium.
As water heats inside the tank, these minerals separate and settle to the bottom.
Over time, sediment accumulates into a thick layer that acts like insulation between the heat source and the water.
This forces the water heater to:
- Run longer
- Use more energy
- Heat less efficiently
Heavy sediment buildup can also:
- Overheat tank bottoms
- Damage heating elements
- Create noisy operation
- Reduce hot-water capacity
The best practice is to flush several gallons from the tank once a year.
Homes with hard water may benefit from more frequent flushing.
Electric and gas water heaters both accumulate sediment at the bottom of the tank. © Don Vandervort, HomeTips
How to Flush or Drain a Water Heater
Safety Warning:
Water inside a water heater can be extremely hot and may cause serious burns. Allow the heater to cool before draining if possible.
1. Turn Off the Water Heater
For an electric water heater:
- Turn off the circuit breaker supplying power
For a gas water heater:
- Turn the gas control valve to “Pilot” or “Off”
This prevents the heating elements or burner from operating while the tank is partially empty.
Important: Never operate an electric water heater with the tank partially empty because the heating elements can burn out quickly.
2. Turn Off the Cold-Water Supply Valve
Locate the cold-water inlet pipe above the water heater.
This pipe usually enters near the top of the tank and often feels cooler than the hot-water outlet pipe.
Turn the shutoff valve clockwise to close it.
If the valve uses a lever handle, turn it perpendicular to the pipe.
This shutoff valve controls the incoming cold-water supply to the water heater. © Don Vandervort, HomeTips
3. Connect a Garden Hose to the Drain Valve
The drain valve is located near the bottom of the tank.
It usually resembles a small outdoor hose faucet.
Attach a standard garden hose securely to the drain valve threads.
Run the other end of the hose to:
- A floor drain
- A utility sink
- Outdoors
- A large bucket
Make sure the hose end is lower than the drain valve so gravity can drain the tank properly.
Attach a garden hose to the drain valve before opening it. © Don Vandervort, HomeTips
4. Open a Hot-Water Faucet
Open a hot-water faucet somewhere in the house.
This allows air into the plumbing system and helps prevent a vacuum from forming inside the tank.
You can also carefully lift the handle on the:
- Temperature-pressure relief valve (TP valve)
The TP valve is the brass safety valve located near the top or upper side of the water heater.
Opening it allows air into the tank so water drains more smoothly.
5. Open the Drain Valve
Carefully open the drain valve by turning it counterclockwise.
Hot water will begin flowing through the hose.
If you are simply flushing sediment:
- Drain about 3 to 5 gallons
- Continue until water runs relatively clear
If you are completely draining the tank:
- Leave the valve open until the tank empties fully
Some sediment may appear as:
- Cloudy water
- Brown particles
- White mineral flakes
6. Flush Fresh Water Through the Tank
For a better sediment flush:
- Turn the cold-water supply valve on briefly
- Then shut it off again
This incoming water stirs up sediment at the bottom of the tank and helps flush it out through the hose.
Repeat this process several times until the draining water appears cleaner.
Don’s Advice
Don’t expect perfectly clear water if the heater has significant mineral buildup.
The goal is to remove as much loose sediment as possible without damaging old components.
7. Close the Drain Valve
Once flushing is complete:
- Close the drain valve firmly
- Remove the garden hose
Do not overtighten plastic drain valves because they can crack.
8. Refill the Tank
Close the hot-water faucet that you opened earlier.
Then reopen the cold-water supply valve to refill the tank.
As the tank fills:
- Air will sputter from hot-water faucets
- Water may appear cloudy briefly
Allow a hot-water faucet to run until air bubbles stop and water flows smoothly.
9. Restore Power or Gas
After the tank is completely full:
- Turn the circuit breaker back on for electric heaters
- Relight or restart the gas heater according to manufacturer instructions
Important: Always verify the tank is completely full before restoring power to an electric heater.
Water Heater Won’t Drain
If little or no water flows from the drain valve, sediment may be clogging the opening.
This is common on older water heaters that have not been flushed regularly.
1. Open the Pressure-Relief Valve
Opening the TP valve may break a vacuum that is preventing water from draining.
Use caution because hot water may discharge from the valve.
2. Try Pulsing the Hose
If the drain valve seems clogged:
- Step briefly on the garden hose several feet from the heater
- Then release quickly
This can force water pressure backward momentarily and sometimes loosen sediment blocking the valve.
Heavy sediment buildup can clog the drain valve opening. ©Don Vandervort, HomeTips
3. Back-Flush the Tank
If the valve remains clogged, back-flushing may clear the obstruction.
How to Back-Flush a Water Heater
Back-flushing forces water backward through the drain valve to loosen sediment.
You will need:
- A garden hose
- A double-female hose connector
1. Close the Water Heater Drain Valve
Turn the drain valve clockwise to close it fully.
2. Connect the Hose to a Faucet
Using the double-female hose coupler, connect one end of the hose to an outdoor faucet or laundry faucet.
A double-female hose coupler allows two male hose fittings to connect together. Bosch
3. Charge the Hose With Water Pressure
Turn on the faucet briefly to fill the hose with water pressure.
4. Open the Water Heater Drain Valve
Open the drain valve carefully.
Pressurized water should flow backward into the tank and help dislodge sediment near the valve opening.
5. Try Draining the Tank Again
Disconnect the hose and try flushing the tank normally again.
If the drain still clogs repeatedly, the drain valve may need replacement.
How to Replace a Water Heater Drain Valve
Sometimes sediment buildup damages or permanently clogs the drain valve.
Replacement valves are inexpensive and available at most hardware stores.
Replacement drain valves are inexpensive and widely available. B&K
Caution:
Replacing a drain valve can release large amounts of water quickly. Be prepared for spills and use caution around hot water.
1. Shut Off Water and Power
Turn off:
- The cold-water supply valve
- Electrical power or gas supply
Allow the tank to cool as much as possible.
2. Wrap the New Valve Threads
Apply Teflon® tape or pipe-thread sealant to the replacement valve threads before installation.
3. Remove the Old Valve
Using a pipe wrench, turn the old valve counterclockwise.
As the valve loosens, water may begin leaking or spraying.
Have:
- Buckets
- Towels
- A helper if possible
4. Clear Heavy Sediment
If heavy sediment blocks the opening:
- Insert a screwdriver carefully into the opening
- Break up mineral deposits
Be prepared for water flow to increase suddenly.
5. Install the New Valve
Thread the new valve into the opening and tighten it securely.
The outlet should point downward for hose connection.
6. Test the Valve
Open and close the new valve several times.
Then flush additional sediment from the tank until water runs cleaner.
7. Refill and Restart the Water Heater
Refill the tank fully before restoring electrical power or gas operation.
Need Professional Help?
If the drain valve is leaking badly, the tank is heavily corroded, or the repair becomes complicated, a licensed plumber may be the safest option.
Find a trusted local plumber for water heater repairs or replacement.
FAQs
How often should a water heater be flushed?
Most water heaters should be flushed once a year. Homes with hard water may benefit from more frequent flushing.
Can flushing a water heater cause leaks?
Occasionally, flushing an old neglected tank may expose existing corrosion problems that were hidden by sediment buildup.
Why is my water heater making popping sounds?
Sediment buildup at the bottom of the tank commonly causes rumbling or popping noises during heating.
How long does it take to flush a water heater?
A basic flush usually takes 30 to 60 minutes, depending on sediment buildup and tank size.
Should I completely drain the tank?
For routine maintenance, flushing several gallons is usually sufficient unless repairs require full draining.
Why won’t my water heater drain?
The drain valve is often clogged with sediment or mineral deposits.
