How to Safely Shut Off Your Water Heater
Shutting off a water heater requires a specific order of operations. Turn things off in the wrong sequence and you risk burning out heating elements, cracking the tank, or creating a scalding hazard. This guide covers the safe procedure for both gas and electric models.
Time Required
5 - 10 minutes
Difficulty
Easy to Moderate
Help Needed
None — fully DIY (call gas company if you smell gas)
The Critical Rule: Energy Off Before Water Off
This is the single most important thing to remember about water heater shutoffs. Getting the order wrong can destroy your water heater.
Warning: Never turn off water with the heater still running
If the tank loses water while the heating element or gas burner is still active, the result is called "dry firing." For electric heaters, the exposed heating element will burn out within minutes — a $150 to $300 repair. For gas heaters, the burner can overheat the empty or low tank, cracking the glass lining and potentially warping the tank itself. A cracked lining means the entire tank needs replacement.
Always follow this order: (1) Turn off gas or electricity, (2) Then turn off the water supply.
Shutting Off a Gas Water Heater
Gas water heaters have a dedicated gas control valve on the front of the unit near the bottom. This is separate from any gas shutoff valve on the gas supply line.
Locate the gas control knob
On the front of the water heater near the bottom, you will find a rectangular box with a knob that has three positions: ON, PILOT, and OFF. This is the gas control valve (sometimes called the thermostat).
Turn the knob to OFF (or PILOT for short shutoffs)
For a complete shutoff (draining, repairs, vacation), turn the knob to OFF. For a short-term shutoff where you want to keep the pilot light burning, turn it to PILOT. The PILOT position keeps a small flame lit so you do not have to relight it later.
Close the gas supply valve (for extended shutoffs)
If you are turning off the heater for more than a day, also close the gas shutoff valve on the gas supply pipe. This is a separate valve on the gas line leading to the unit — turn the lever perpendicular to the pipe. This provides a second layer of safety.
Turn off the cold water inlet valve
Now that the gas is off, close the cold water supply valve on top of or just above the water heater. This stops new water from entering the tank. For ball valves, turn the lever perpendicular to the pipe. For gate valves, turn clockwise until it stops.
If you smell gas at any point — stop immediately
Do not touch any switches, light any flames, or use your phone near the water heater. Leave the house immediately, go to a safe distance, and call your gas utility company's emergency line or 911. A gas leak requires professional response — this is never a DIY situation.
Shutting Off an Electric Water Heater
Electric water heaters are simpler to shut off, but the same energy-first-then-water rule applies. The key is finding the correct circuit breaker.
Find the water heater breaker in your electrical panel
Open your main electrical panel (breaker box). Look for a double-pole 30-amp breaker labeled "Water Heater," "WH," or "HW Heater." It will be a larger breaker that takes up two slots. If breakers are not labeled, it is typically one of the larger breakers (30A) in the panel.
Switch the breaker to the OFF position
Flip the breaker firmly to OFF. The breaker should click into position. If it feels loose or does not stay in the OFF position, the breaker itself may need replacement — call an electrician.
Verify power is off (optional but recommended)
If you have a non-contact voltage tester, hold it near the electrical conduit connection on the side of the water heater. It should not beep or light up. This confirms the correct breaker was turned off. This step is especially important if your breakers are not well labeled.
Turn off the cold water inlet valve
With the electricity confirmed off, close the cold water supply valve above the water heater. This is the same procedure as for gas heaters — turn the valve handle clockwise or perpendicular to the pipe.
Relieving Pressure After Shutoff
After turning off both the energy source and the water supply, you may need to relieve pressure in the tank before performing any work.
Steps to Relieve Pressure
- Open a hot water faucet: Go to any sink or tub and turn on the hot water side only. Water will flow briefly and then stop as air enters the system. Leave this faucet open — it acts as a vent while you work.
- Lift the T&P relief valve lever (if draining): The temperature and pressure (T&P) relief valve is on the side or top of the tank with a small lever and a discharge pipe pointed downward. Lift the lever briefly to release pressure. Be careful — water coming out will be very hot.
- Wait for the water to cool: If you need to drain the tank or disconnect any plumbing, wait 1 to 2 hours for the water inside to cool. Water in a heater can be 120 to 140 degrees Fahrenheit — hot enough to cause serious burns in seconds.
Good to know: The tank stays full even when shut off
Turning off the cold water inlet valve does not drain the tank. The tank will remain full of water (30 to 80 gallons depending on your model) until you actively drain it through the drain valve at the bottom. For most plumbing repairs elsewhere in the house, you do not need to drain the water heater — you only need to shut it off to protect the heating elements.
Restarting Your Water Heater Safely
When you are ready to turn the water heater back on, follow this sequence carefully. The goal is to ensure the tank is full of water before the heating element or burner activates.
Open the cold water inlet valve
Turn the cold water supply valve back on. You will hear water flowing into the tank. If the tank was drained, this will take several minutes to fill completely.
Open a hot water faucet and wait for steady flow
Run a hot water faucet until water flows steadily with no air sputtering or burping. This confirms the tank is full and all air has been purged from the lines. This step is critical — do not skip it.
Turn on the energy source
For electric heaters, flip the breaker back on. For gas heaters, turn the gas control knob to PILOT, relight the pilot if needed (follow the instructions on the unit's label), then turn to ON and set your desired temperature (120 degrees Fahrenheit is the recommended setting).
Wait 30 to 60 minutes for hot water
A full tank of cold water takes 30 to 60 minutes to heat up (gas heaters are faster than electric). Check a hot water faucet periodically. If you have hot water, the restart was successful.
Pro Tips
- •Label your water heater breaker: If it is not already labeled, put a piece of tape on the breaker and write "WATER HEATER" on it now. During an emergency, you do not want to flip random breakers hoping to find the right one.
- •Set your thermostat to 120 degrees Fahrenheit: Many water heaters ship set to 140 degrees, which wastes energy and increases scald risk. Check the dial on the gas control valve or the thermostat behind the access panels on electric heaters. The Department of Energy recommends 120 degrees.
- •Know your tank size: Look at the rating plate on the side of your water heater — it lists the tank capacity in gallons. This tells you how long refilling will take and how long you will wait for hot water after a restart. A 50-gallon gas heater recovers in about 40 minutes; a 50-gallon electric heater takes about 60 to 80 minutes.
Frequently Asked Questions
What happens if I turn off the water but not the heater?
If you turn off the water supply without turning off the energy source (gas or electric), the water heater will continue to heat the remaining water in the tank. If the tank drains or runs low, the heating element or burner can overheat, a condition called dry firing. For electric heaters, this can burn out the heating elements within minutes. For gas heaters, it can crack the glass lining inside the tank, permanently ruining the unit. Always turn off the energy source first.
How do I know if my water heater is gas or electric?
A gas water heater has a gas line (usually a yellow or black pipe) connected to a burner assembly at the bottom of the tank, and a vent pipe or flue on top. You may also see a pilot light window near the bottom. An electric water heater has no gas line or flue. Instead, it has one or two electrical conduit connections on the side of the tank and a dedicated circuit breaker in your electrical panel, usually labeled "Water Heater" as a 30-amp double-pole breaker.
Do I need to shut off my water heater if I turn off the main water supply?
Yes. Anytime the water supply to the tank could be interrupted — whether you turn off the main shutoff, the water heater inlet valve, or the city shuts off water for maintenance — you should turn off the energy source to the water heater. This prevents dry firing if the tank loses water. For short shutoffs (under 30 minutes), the risk is low but it is still best practice to turn off the heater.