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  #1  
Old 06-28-2011, 11:00 AM
sevenwood sevenwood is offline
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Shutting off my main water valve will cause my hot water heater to fail?

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!
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  #2  
Old 06-28-2011, 11:04 AM
Baracus Baracus is offline
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You could just flip the breaker to the water heater.
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Old 06-28-2011, 11:05 AM
silenus silenus is offline
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If you are that worried about it, just shut off the water heater when you shut off the water. No sweat.
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  #4  
Old 06-28-2011, 11:10 AM
Joey P Joey P is offline
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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.
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  #5  
Old 06-28-2011, 11:32 AM
Xema Xema is offline
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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.
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  #6  
Old 06-28-2011, 11:32 AM
kayaker kayaker is offline
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Shutting off the breaker to the water heater also gives you the chance to drain it.
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  #7  
Old 06-28-2011, 11:41 AM
cornflakes cornflakes is offline
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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.)
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  #8  
Old 06-28-2011, 12:12 PM
dracoi dracoi is offline
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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.
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  #9  
Old 06-28-2011, 12:13 PM
Machine Elf Machine Elf is offline
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Quote:
Originally Posted by sevenwood View Post
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.
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  #10  
Old 06-28-2011, 12:24 PM
anson2995 anson2995 is offline
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Quote:
Originally Posted by Machine Elf View Post
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.
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  #11  
Old 06-28-2011, 12:26 PM
sevenwood sevenwood is offline
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Thanks all.

Many of you said:

Quote:
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.

Last edited by sevenwood; 06-28-2011 at 12:31 PM.. Reason: added last sentence
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  #12  
Old 06-28-2011, 12:28 PM
johnpost johnpost is offline
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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.

Last edited by johnpost; 06-28-2011 at 12:31 PM.. Reason: was assuming electric and typing went gas was revealed
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  #13  
Old 06-28-2011, 12:32 PM
Joey P Joey P is offline
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Quote:
Originally Posted by sevenwood View Post
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.

Last edited by Joey P; 06-28-2011 at 12:34 PM..
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  #14  
Old 06-28-2011, 12:46 PM
kanicbird kanicbird is offline
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Quote:
Originally Posted by sevenwood View Post
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.



Quote:
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.

Last edited by kanicbird; 06-28-2011 at 12:47 PM..
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  #15  
Old 06-28-2011, 01:23 PM
sevenwood sevenwood is offline
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Quote:
Originally Posted by Joey P View Post
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!
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  #16  
Old 06-28-2011, 10:50 PM
Kiwi Fruit Kiwi Fruit is online now
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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 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.
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  #17  
Old 06-28-2011, 10:51 PM
TriPolar TriPolar is offline
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OK, who's got sevenwood's address? We've got to go mess with his hot water heater while he's on vacation

Last edited by TriPolar; 06-28-2011 at 10:52 PM..
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  #18  
Old 06-29-2011, 08:36 PM
handsomeharry handsomeharry is online now
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Quote:
Originally Posted by TriPolar View Post
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
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  #19  
Old 06-30-2011, 10:13 PM
thelabdude thelabdude is offline
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Originally Posted by cornflakes View Post
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.
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