How to Drain a Water Heater
To drain a water heater, turn off the gas or power, shut the cold water supply, connect a garden hose to the drain valve at the bottom of the tank, open a hot water tap in the house, and then open the drain valve. Draining typically takes 20 to 40 minutes, longer if the tank is full of sediment.
You'll drain heater water like this before a flush, a replacement, a vacation home shutdown or an anode rod swap. The steps below are based on A.O. Smith's instructions.
Tools you'll need
- A garden hose long enough to reach a floor drain or outside
- A bucket if no drain is close
- A flathead screwdriver, since many drain valves have a slotted stem
- Thick gloves and safety goggles
- Towels or rags
- Optional: an adjustable wrench and a wet/dry vacuum for stubborn sediment
Steps to drain the tank
Shut off the heat
On an electric heater, switch off the breaker. On a gas heater, set the gas control dial to OFF. If you can, wait a few hours for the water to cool.
Close the cold water supply
It's the valve on the cold pipe going into the top of the tank. If it won't hold, use the main shutoff.
Hook up the hose
Thread the hose onto the drain valve near the bottom of the tank and run the other end to a floor drain, outside, or into a bucket. The far end has to be lower than the valve or the water won't flow.
Open a hot tap
A.O. Smith says to open a hot faucet in the house to relieve pressure. You'll get a gush, then a trickle. If water keeps flowing normally, the cold valve isn't fully closed. Leaving that tap open lets air into the tank so it drains faster.
Open the drain valve
Turn it by hand or with a screwdriver. If you're using a bucket, empty it before it overflows.
Wait
Figure 20 to 40 minutes for a full tank.
The plastic drain valves on many tanks are the weak point here. Turn them gently and don't force them past where they stop.
Draining part of the tank
You don't always need to empty it. A.O. Smith's troubleshooting guide suggests draining a few gallons once a year to remove sediment before it builds up. For that, skip the cold-supply shutoff, put a bucket under the valve, and open it until the water runs clear. Leave the heat off while you do it.
Refilling and restarting
Close the drain valve and remove the hose.
Open the cold water supply with a hot tap still open.
Let the tap run until you get a steady flow without air bubbles. That means the tank is full. A.O. Smith says to let it run at least 3 minutes to clear trapped air.
Turn the breaker back on, or turn the gas on and relight the pilot following the label on the tank.
Never turn on an empty electric heater, because that damages the heating elements. Our turning on a water heater page covers relighting a gas unit.
Hot water tank won't drain
The usual culprit is sediment. Scale flakes and grit settle at the bottom and plug the drain valve. A.O. Smith says sediment can keep a tank from draining fully.
Things to try:
- Make sure a hot tap is open. A tank with no air coming in drains slowly or not at all.
- Close the drain valve, briefly open the cold supply to stir up the bottom, then try again.
- Check the hose for a kink or a high spot.
If the valve is clogged and won't clear, A.O. Smith recommends calling a plumber or service technician rather than forcing it. A broken plastic drain valve on a full tank is a much bigger mess than a slow drain.
How to empty a water tank fast
There's no real shortcut, but a few things help. Use a full-size hose with no kinks and send it downhill. Keep a hot tap open upstairs. If the tank sits below the drain, a small transfer pump on the hose speeds things up. Don't remove the drain valve on a full tank to "speed it up."
Draining a tankless water heater
A tankless heater has no tank to drain. To empty one for freeze protection or service, you close the hot and cold isolation valves and open the purge or drain ports, following the steps in the manual. Condensing tankless units also have a condensate drain line. That line carries acidic water from the exhaust and should run to a drain without sags or kinks. If it clogs, the unit may shut down. For the yearly descale, see how to flush a tankless water heater.
Draining an RV hot water tank
RV tanks are smaller and drain through a plug or the anode rod opening on the outside wall of the camper. Turn off the heater and water pump, open the pressure relief valve, then remove the plug. The exact fitting depends on the brand, so check the RV heater's manual.
No hot water after draining
If the heater won't heat after a drain:
- Electric: It may have been turned on before it was full, which damages the elements. Also check whether the reset button tripped. A.O. Smith says to press it firmly until it clicks.
- Gas: The pilot may need relighting, or the gas valve is still on OFF.
- Both: Give it time. A refilled tank takes a while to heat.
If none of that works, start at our no hot water guide.
When to hire it out
If the drain valve is plastic and the tank is old, think about having a plumber do it. They can swap in a brass drain valve while the tank is empty. HomeGuide puts a professional flush at $75 to $250.
FAQ
How long does it take to drain a water heater?
A.O. Smith says 20 to 40 minutes is typical, and longer with heavy sediment. Add time up front to let the water cool.
Do you need to turn off the water to drain a water heater?
Yes. Close the cold supply to the tank, or the main if that valve won't seal. Otherwise the tank keeps refilling as it drains.
Why open a hot water faucet when draining?
It relieves the pressure in the tank and lets air in. Without it, the tank drains slowly or stalls.
Should I drain my water heater every year?
Flush it at least once a year, more often with hard water. A full drain-and-flush clears sediment that shortens tank life. See how to flush a water heater.
Sources
- A. O. SmithHow to Drain and Flush a Water Heater (opens in a new tab)
- A. O. SmithWater Heater Installation Guide (opens in a new tab)
- A. O. SmithWater Heater Not Working? Troubleshooting Guide (opens in a new tab)
- HomeGuideWater Heater Repair Cost (opens in a new tab)