How to Turn Off a Water Heater (Gas and Electric)

Turning off an electric water heater

The most important rule with an electric heater: if you turn off the water and might drain the tank, turn off the power too. A.O. Smith warns that turning on an empty electric water heater damages the heating elements. When the water's back on, refill the tank completely before you restore power.

Turning off a gas water heater

Many gas controls also have a VACATION or low setting. That keeps the pilot lit and holds the water warm without heating it to full temperature. It's handy for a short trip, and it saves you relighting the pilot when you get home.

Turning a gas heater off at the dial leaves the gas line pressurized up to the valve. That's normal. If you're removing the heater, A.O. Smith says to shut off the main gas supply before disconnecting lines.

The hot water heater shutoff valve

The water shutoff for the heater is on the cold water inlet pipe at the top of the tank. It's either a lever handle (a ball valve) or a round wheel (a gate valve). The lever is closed when it's crosswise to the pipe. The wheel turns clockwise to close.

Old gate valves often don't seal all the way, and some break if forced. If the valve won't hold, close the main shutoff for the house; A.O. Smith's draining guide names the main as the other way to stop the supply. Know where yours is before you need it.

Closing the cold inlet stops new water from entering the tank. It doesn't empty the tank, and hot water will still come out of a tap for a moment until pressure drops.

Turning off a tankless water heater

Tankless units shut off the same way in principle:

• Turn off the power at the breaker, or at the unit's own switch if it has one.
• Close the gas supply valve on gas models.
• Close the cold (blue) and hot (red) isolation valves if you need the water off at the heater. A.O. Smith says they're closed when the handles sit perpendicular to the pipes.

If the unit is outside or in an unheated space and you're shutting it down for winter, follow the manual's freeze-protection steps. A tankless heater full of water can freeze and crack.

When to turn it off

• A leak. Heat off first, then the water. Then see water heater leaking.
• Draining or flushing. Both shutoffs. Our drain and flush guides cover the rest.
• Plumbing work elsewhere in the house. If the main is going off, turn off an electric heater too, in case the tank drains.
• A vacation. Gas: VACATION setting or OFF. Electric: breaker off. You'll save the energy of keeping a full tank hot.
• Any work on the heater itself. Always.

Mistakes to avoid

• Turning the water off but leaving an electric heater on while plumbing is drained. That's how elements burn out.
• Forcing an old gate valve. Use the main if it won't close.
• Relying on the panel label. Test before you touch.
• Blowing out the pilot to "turn it off." Use the gas control dial.

Why does my hot water tank keep shutting off?

If the heater goes off on its own, it isn't a shutoff problem. It's a fault:

• Electric: A tripped breaker or a tripped reset button. A.O. Smith says repeated tripping of the reset button points to serious problems and calls for a professional. See water heater reset button.
• Gas: A pilot that goes out. Check that the gas valve is open and the pilot lit. If it won't stay lit, see pilot light won't stay lit.
• Tankless: An ignition failure. A.O. Smith says to check the gas supply, venting and ignition parts, which may need a pro.