Should You Turn Off the Water Heater If Water Is Off?
On this page (5 sections)
The Short Answer: For a short water outage with the plumbing left intact, a tank water heater normally stays full and can be left on. Turn it off if the pipes will be drained, work is being done on the heater or nearby pipes, the outage will be long, or you are unsure. When water returns, refill and purge air from a hot tap before turning the heater back on.
Why a full tank is usually fine
A water heater tank only empties if water can leave and air can get in. With the street supply off and the house plumbing closed, opening a hot tap gives a short burst and then stops, because nothing pushes water out. The tank stays essentially full, and heating it is no different from a night with no hot water use.
When to turn it off
Turn the heater off when any of these apply:
- The plumbing will be drained, for a repair, a re-pipe, or winterizing. Opening low drains and high faucets lets the tank lose water.
- Someone is working on the heater or the pipes connected to it.
- There is a leak at the heater or nearby, or you need to drain the tank.
- A long outage, or one where you cannot be sure what others in the building will do (shared buildings, rentals).
The cost of turning it off is a little time to reheat. The cost of an electric element heating in air is a burned-out element. A gas burner firing on a tank that has lost water can overheat the tank and trip its safety limit.
How to turn it off
| Heater type | How |
|---|---|
| Electric tank | Switch off the double-pole breaker for the heater |
| Gas tank | Turn the gas control knob to OFF (or to PILOT if you want to avoid relighting and the tank will stay full); follow the label on the heater |
| Heat pump water heater | Switch off its breaker |
| Gas tankless | Turn it off at the controller. Keep its power on in freezing weather if it still holds water, because freeze protection needs electricity. If it will be drained, power can be turned off. |
| Electric tankless | Switch off its breakers if the lines will be drained |
If the heater is in an apartment building, see how to turn off a water heater in an apartment.
Turning it back on
- Open the cold-water supply valve to the heater.
- Open a hot tap (a tub spout works well) and let it run until water flows steadily with no air sputtering. This confirms the tank is full.
- Then restore power, or relight or turn the gas control back to ON following the label.
- Expect some cloudy or rusty-looking water at first after a street outage; run cold taps until it clears.
For electric tanks, never restore power until the hot tap runs steadily. If you think a heater ran without water, see water heater turned on without water before resetting anything; a burned-out element or tripped high-limit needs proper diagnosis.
Frequently Asked Questions
Q: Can my water heater explode if the water is off? A: Not from the supply being off. The tank still has its relief valve and temperature limits. The real risks are damaging an electric element or overheating a tank that has lost water.
Q: The water is back, but now I have no hot water. What happened? A: On electric tanks, a tripped high-limit or a burned element is common if it ran low on water. On gas, the pilot may have gone out or air in the water lines may be the issue. Start with no hot water after flushing, which covers the same restart problems.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith: standard electric no-hot-water diagnostic chart (opens in a new tab)Professional diagnostic context for standard electric storage heaters; not instructions to open or test your appliance.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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