How to Drain a Water Heater

Water heaters require relatively little maintenance but should be drained once a year to flush out sediment. Knowing how to drain a hot water heater helps keep the tank clean and extends its working life. Here’s how to give your water heater some annual attention.

Why You Should Drain Your Water Heater

Naturally occurring minerals in water and foreign bodies such as sand and grit settle in the bottom of water heater tanks over time. Sediment is more likely to build up in hard water than in soft water.

Sediment buildup reduces the unit’s efficiency and can damage the tank’s internal components. Sediment can also clog the unit’s pressure relief valve, compromising the water heater's safety.

Regular tank draining flushes out sediment, extends the water heater's lifespan, improves the unit’s efficiency, and provides better water quality.

When to Drain Your Water Heater

Water heaters should be drained once a year. Signs that indicate it’s time to drain your water heater include:

Noisy operation (popping sounds inside tank)
Fluctuating water temperature
Reduced hot water supply

Tools and Materials Needed

To flush a gas or electric water heater, you need the following tools:

Garden hose
Bucket or nearby floor drain
Adjustable wrench
Screwdriver
Teflon tape
Towels or rags

If you have a tankless water heater, you’ll need a tankless water heater flushing kit, which includes hoses, buckets, and a circulation pump. You’ll also need undiluted white vinegar.

Step-by-Step Guide to Draining a Water Heater

To drain a conventional gas or electric water heater, take the following steps:

Shut off the water supply valve at the top of the water heater.
Turn off the power from your home’s electrical panel for electric heaters. For gas-powered heaters, check your owner’s manual. Some manufacturers recommend setting the thermostat to pilot, while others ask you to shut off the gas supply to the heater. Follow the instructions outlined in the manual.
Let the water cool overnight as the tank contents are extremely hot.
Place one end of a garden hose into a floor drain or position it outside. Attach the other to the drain valve at the bottom of the tank and open the valve.
Let the tank drain, then turn the water supply back on to flush the tank with clean water.
Turn off the water supply, remove the hose, and close the valve.
Refill the tank.
Turn on the power or the gas supply to the heater.

For help, check out this helpful video on how to drain a hot water heater.

How to Drain a Tankless Water Heater

Draining a tankless water heater is more complicated, and you may prefer to have a professional plumber do the job. To flush the unit yourself, follow the following steps.

Turn off the unit’s main gas valve or the heater’s circuit breaker.
Close and turn off the three water valves connected to the heater.
Remove the purge port valve caps after checking that the cold and hot water valves are closed.
Attach the hose lines from your tankless heater flushing kit to the water valves (the manufacturer may have provided these with the tank).
Twist the purge port valves to open them.
Follow your owner’s manual instructions to flush and drain the heater with undiluted white vinegar.
Close the purge port valves
Disconnect the hosing lines.
Return the purge port valve caps to the three water valves.
Restart the heater.
Turn on a tap and run the hot water until there is no more air in the pipes.

Post-Drain Maintenance Tips

What to Do if the Drain Valve Is Clogged

Water pressure often fixes a clogged drain valve, so wait a few minutes after opening it. If this fails, close the valve, remove the hose, use a stiff wire to break down sediment in the valve, then try again. Another option is to stomp on the hose about two feet away from where it connects to the open valve. Doing so can force air bubbles into the tank, potentially unclogging the valve.

If this fails, connect one end of a hose to the valve and the other to a faucet. Open the valve, turn on the water, and let it flow into the tank for about 15 seconds. If this fails to move the clog, contact Roto-Rooter.

How to Handle a Stuck Pressure Relief Valve

The pressure relief valve of a water heater is a safety device that prevents excess heat and pressure from building up in the tank. If the valve is stuck, turn off the heater and let the tank water cool. Spray the pressure relief valve threads with penetrating oil and let it soak in for a few minutes. Slightly tighten the valve, spray the threads again, and wait a bit longer. Now, loosen the valve and spray the oil as you work it back and forth.

Dealing with Persistent Sediment Buildup

If you need to flush sediment out of your water heater more than once a year, contact a professional plumber for assistance. The heater may need servicing or replacing. You should let a professional flush the tank if it has not been drained for three or more years.

How Long Does It Take to Drain a Water Heater

Depending on the size of the tank, it can take 5 to 10 minutes to drain a water heater.

How to Drain a Hot Water Heater Quickly

Opening a hot water tap close to the water heater helps the tank drain faster, especially if the tap is on a floor above the heater.

Remember, safety is key when draining a water heater. If improperly handled, tank water, heating elements, and power supplies can cause injury. If you’d prefer not to drain your tank yourself, contact Roto-Rooter today, and one of our friendly, professional technicians will drain and flush your heater for you.