# Shutting off my main water valve will cause my hot water heater to fail? **URL:** \ **Category:** Factual Questions\ **Created:** [June 28, 2011, 4:00pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150 "2011-06-28T16:00:43Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![sevenwood](https://avatars.discourse-cdn.com/v4/letter/s/6de8d8/32.png) [@sevenwood](https://boards.straightdope.com/u/sevenwood)\ **Post date:** [June 28, 2011, 4:00pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/1 "2011-06-28T16:00:43Z")
That’s what my friend claims, and I’m reluctant to shut off my main water valve unless I find out that he’s wrong. Help! We’re going to go on vacation for a couple of weeks, and I’d planned to shut off the main water valve in the house just before we left. I mean, why risk coming home to a basement full of water? But my friend told me that if I did that, my hot water heater (which is 16 years old) could overheat and burn out. I don’t want to risk that. So what can I do that is relatively safe? We don’t want to shut off the electricity to the whole house because, well, that would keep our DVR from recording those all-important television specials! ---
**Author:** ![Baracus](https://avatars.discourse-cdn.com/v4/letter/b/2bfe46/32.png) [@Baracus](https://boards.straightdope.com/u/Baracus)\ **Post date:** [June 28, 2011, 4:04pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/2 "2011-06-28T16:04:47Z")
You could just flip the breaker to the water heater. ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [June 28, 2011, 4:05pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/3 "2011-06-28T16:05:41Z")
If you are that worried about it, just shut off the water heater when you shut off the water. No sweat. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [June 28, 2011, 4:10pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/4 "2011-06-28T16:10:32Z")
The only way your water heater could fail is if you blew a leak somewhere in the system that caused the water heater to drain. I suppose, given enough time, the water could evaporate (steam) out of a leak somewhere else in the system, but I wouldn’t count on that. But yeah, just shut off the breaker to the water heater and don’t worry about it. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [June 28, 2011, 4:32pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/5 "2011-06-28T16:32:21Z")
There is no value in having the water heater working while you are gone - a complete waste of energy. When you return, flip the breaker back on and you’ll have hot water in something like 20 minutes. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [June 28, 2011, 4:32pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/6 "2011-06-28T16:32:41Z")
Shutting off the breaker to the water heater also gives you the chance to drain it. ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [June 28, 2011, 4:41pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/7 "2011-06-28T16:41:15Z")
Wit the main valve and the outlets closed, the home plumbing will become a closed system, and **maybe** , the cycling of the water heater will cause enough of a change in pressure that there will be some venting of steam through the T&P valve, and this eventually could cause the heater tank to run dry, burning the out elements. But my guess is that this won’t happen in a couple of weeks. All the same, shut the heater off while you’re away. This way, you can guarantee that the heater won’t cycle the pressure in your pipes (which probably won’t matter, but it isn’t a good idea.) ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [June 28, 2011, 5:12pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/8 "2011-06-28T17:12:39Z")
Just to state the obvious: a water heater will fail if the heating element is not covered with water. Everyone’s responses are based on that knowledge, but I’ve learned not to make any assumptions on the Internet. So, as others have said, if you shut off the water and not the power to the water heater, there are conceivable scenarios where the water level falls and the heating element dies. These scenarios are not all that likely, but it’s good practice to turn off the power to a water heater when you’re going to be gone for some time. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 28, 2011, 5:13pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/9 "2011-06-28T17:13:29Z")
> [@sevenwood](#): > > That’s what my friend claims, and I’m reluctant to shut off my main water valve unless I find out that he’s wrong. Help! > > We’re going to go on vacation for a couple of weeks, and I’d planned to shut off the main water valve in the house just before we left. I mean, why risk coming home to a basement full of water? But my friend told me that if I did that, my hot water heater (which is 16 years old) could overheat and burn out. I don’t want to risk that. Your water heater will not overheat because - are you ready for this amazing factoid? - it’s equipped with a _thermostat_. When the water in the tank reaches its target temperature, the thermostat will turn off the power to the heating element. When the water cools off a smidge, the thermostat will turn the power back on. This cycle has been carrying on since you moved in, and will continue even in your absence. The water heater and its thermostat do not care whether you’ve closed the main water valve or not. People Who Know About These Things recommend that water heaters be set to keep water at 120-140 degrees Fahrenheit. This is nowhere near the boiling point of water (212F), so even if your pipes somehow spring a leak while you’re gone (why this would happen, I don’t know), the water heater would never be expected to boil off any water from the tank. You’d have to develop a leak at the bottom of the tank in order to empty it. We have a gas-powered water heater, and I always shut the main water valve when we leave on vacations. The water heater is just fine. ---
**Author:** ![anson2995](https://avatars.discourse-cdn.com/v4/letter/a/c77e96/32.png) [@anson2995](https://boards.straightdope.com/u/anson2995)\ **Post date:** [June 28, 2011, 5:24pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/10 "2011-06-28T17:24:04Z")
> [@Machine\_Elf](#): > > so even if your pipes somehow spring a leak while you’re gone (why this would happen, I don’t know), the water heater would never be expected to boil off any water from the tank. You’d have to develop a leak at the bottom of the tank in order to empty it. If there is a small leak, say in the bathtub’s hot water faucet, it could easily drain the hot water tank in a couple of weeks. With the main water supply shut off, the tank would eventually empty, and the heating element could burn out. ---
**Author:** ![sevenwood](https://avatars.discourse-cdn.com/v4/letter/s/6de8d8/32.png) [@sevenwood](https://boards.straightdope.com/u/sevenwood)\ **Post date:** [June 28, 2011, 5:26pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/11 "2011-06-28T17:26:44Z")
Thanks all. Many of you said: > [@](#): > > flip the breaker to the water heater. I guess I should have mentioned that we have a gas water heater, so there’s no breaker exclusively for it (I just looked). However, when I went downstairs to see if there was some sort of local on/off switch to the water heater, I discovered (and I really should have looked first) that it had a rotary temperature dial that says “Hot” on the left side, “Warm” in the middle, and “Vacation” on the right side. I guess I’ll set it to “Vacation” while we’re away. From some of your comments I should also have mentioned that the water heater is in the basement and is at a lower elevation than any of the water outlets (or even any of the pipes - the pipes run along the top of the basement), so unless any leak occurs at the bottom of the water heater it shouldn’t drain the water heater. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [June 28, 2011, 5:28pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/12 "2011-06-28T17:28:11Z")
shut off the circuit breaker or pull the fuses or switch the disconnect for your electric water heater. shutting the water mains off is a good idea not just for your water heater but also for your clothes washer and dishwater, both are connected by hoses that are under pressure and can fail. sinks may also be connected by hoses under pressure that can fail. you could drain your water heater but don’t forget to refill it before turning it back on, place a note at your electrical location you switched it off at. for gas appliances only shut them off if you know how to safely relight them. a vaction setting will only keep the pilot flame lit. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [June 28, 2011, 5:32pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/13 "2011-06-28T17:32:08Z")
> [@sevenwood](#): > > Thanks all. > > Many of you said: > > I guess I should have mentioned that we have a gas water heater, so there’s no breaker exclusively for it (I just looked). However, when I went downstairs to see if there was some sort of local on/off switch to the water heater, I discovered (and I really should have looked first) that it had a rotary temperature dial that says “Hot” on the left side, “Warm” in the middle, and “Vacation” on the right side. I guess I’ll set it to “Vacation” while we’re away. I _assume_ vacation keeps the water heater from firing but also keeps the pilot lit, that would be your best bet. It would also be perfectly acceptable to just shut the gas off. There’s should be a nearby valve. When you get back just follow the instructions printed on the tank for relighting the pilot. ETA, if you use the vacation setting, I’d suggest getting a sharpie or piece of tape to mark where the dial currently is. It’ll make it much easier to get the temperature back to where you want it when you return from vacation. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [June 28, 2011, 5:46pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/14 "2011-06-28T17:46:45Z")
> [@sevenwood](#): > > Thanks all. > > Many of you said: > > I guess I should have mentioned that we have a gas water heater, so there’s no breaker exclusively for it (I just looked). However, when I went downstairs to see if there was some sort of local on/off switch to the water heater, I discovered (and I really should have looked first) that it had a rotary temperature dial that says “Hot” on the left side, “Warm” in the middle, and “Vacation” on the right side. I guess I’ll set it to “Vacation” while we’re away. yes vacation setting should prevent the burner from lighting, just the pilot light. You could also turn it off, but relighting it is a bit tricky if you don’t know how. > [@](#): > > From some of your comments I should also have mentioned that the water heater is in the basement and is at a lower elevation than any of the water outlets (or even any of the pipes - the pipes run along the top of the basement), so unless any leak occurs at the bottom of the water heater it shouldn’t drain the water heater. You could also turn the main almost all the way off, but just open enough to keep a drip or a small stream going to keep the tank pressurized. If you have a leak it will be just dripping, not flooding your house. ---
**Author:** ![sevenwood](https://avatars.discourse-cdn.com/v4/letter/s/6de8d8/32.png) [@sevenwood](https://boards.straightdope.com/u/sevenwood)\ **Post date:** [June 28, 2011, 6:23pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/15 "2011-06-28T18:23:12Z")
> [@Joey\_P](#): > > if you use the vacation setting, I’d suggest getting a sharpie or piece of tape to mark where the dial currently is. It’ll make it much easier to get the temperature back to where you want it when you return from vacation. I just did that - thanks! ---
**Author:** ![Kiwi\_Fruit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kiwi_fruit/32/12_2.png) [@Kiwi\_Fruit](https://boards.straightdope.com/u/Kiwi_Fruit)\ **Post date:** [June 29, 2011, 3:50am UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/16 "2011-06-29T03:50:20Z")
The water will not flow from the water heater when the inlet is shut off. It’s the pressure of the incoming water that allows the faucet to run when you turn it on. This [picture](http://home.howstuffworks.com/water-heater1.htm) shows why. The outlet is in the upper part of the cylinder and goes up. There are drain valves on the bottom of some cylinders and it is conceivable that there could be a leak from that or from a leak in the cylinder itself, but if that’s the case the heater needs replacing anyway. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 29, 2011, 3:51am UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/17 "2011-06-29T03:51:50Z")
OK, who’s got **sevenwood** ’s address? We’ve got to go mess with his hot water heater while he’s on vacation 😃 ---
**Author:** ![handsomeharry](https://avatars.discourse-cdn.com/v4/letter/h/e9c0ed/32.png) [@handsomeharry](https://boards.straightdope.com/u/handsomeharry)\ **Post date:** [June 30, 2011, 1:36am UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/18 "2011-06-30T01:36:56Z")
> [@TriPolar](#): > > OK, who’s got **sevenwood** ’s address? We’ve got to go mess with his hot water heater while he’s on vacation 😃 I think we just did, with all of this fake ‘advice’! Teehee! And he swallowed it whole! Best wishes, hh ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [July 1, 2011, 3:13am UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/19 "2011-07-01T03:13:47Z")
> [@cornflakes](#): > > Wit the main valve and the outlets closed, the home plumbing will become a closed system, and **maybe** , the cycling of the water heater will cause enough of a change in pressure that there will be some venting of steam through the T&P valve, and this eventually could cause the heater tank to run dry, burning the out elements. > > But my guess is that this won’t happen in a couple of weeks. > > All the same, shut the heater off while you’re away. This way, you can guarantee that the heater won’t cycle the pressure in your pipes (which probably won’t matter, but it isn’t a good idea.) This is one of the better posts to this thread. Run some hot water, the tank fills with cold, which expands as it heats. The excess volume has to go somewhere. In the past, it either went back through the main valve if on a public water system or back into the pressure tank if on a well. In most places now, code require a back flow preventer, preventing water from going out the inlet. This has lead to many leaky pressure relief valves. In many cases, the city installed the backflow preventer at the meter without telling the homeowner. The solution is an expansion tank connected between the tank and any valve. You may already have one. If so, shutting the main valve off will have very little effect on the water heater. I just got back from vacation. As I came in, I flipped the breaker for the pump on and turned the valve on the water heater from pilot to on. Once inside, I plugged in the computer. Yes, I have both a whole house surge protector and one at the computer. Unplugging it leaves all 3 wires disconnected. Note, gas safty valves, pressure relief valves, and thermostats fail. ---
**Author:** ![bashdrew](https://avatars.discourse-cdn.com/v4/letter/b/977dab/32.png) [@bashdrew](https://boards.straightdope.com/u/bashdrew)\ **Post date:** [December 21, 2022, 8:49pm UTC](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150/20 "2022-12-21T20:49:50Z")
We will be out for a 5-day vacation and it’s forecast to have a below feeezing point temperature while we’re away. To prevent frozen pipes, can I just turn off the main water valve and leave the water heater on the same setting? Will the water heater get damaged if I leave it on for five days without water coming in? [Next page](https://boards.straightdope.com/t/shutting-off-my-main-water-valve-will-cause-my-hot-water-heater-to-fail/587150.md?page=2)