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I'm a new homeowner so maybe my understanding is off. My question is, why would turning off the cold water intake valve on the top of the heater turn off cold water to the entire house after about 12 hours?

I thought turning off the cold water intake would gradually shut off the hot water, not cold.

Context: We have an ancient (from 1989!) electric water heater in the basement of our townhouse that popped a leak and is going to be replaced, hopefully within a few days, hence me turning it off.

Here's the cold water valve

And here's the entire heater, the valve is at the top in shadow

I turned the power off to our water heater and turned off the cold water intake last night; when I got up this morning, the sinks and the toilets were working fine (except for the hot water obviously) but a few hours later normal water flow to the cold water faucets and the toilets also stopped working (so no flushing!). When we turned the cold water valve to the water heater back on cold water was immediately restored.

VivaLebowski
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  • HI and welcome. Are you on a well? Sounds like you turned off the well pump's power in addition to the HWH. – mike65535 Jan 14 '19 at 16:20
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    Thank you for the greeting and nope; we live in a townhouse that gets city water. The closest thing to a well we have is a sump pump haha. – VivaLebowski Jan 14 '19 at 16:27
  • Simple question: does turning the water back on to the heater restore water to the house? – Machavity Jan 14 '19 at 16:31
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    If the cold water supply to the water heater was turned off, then you'd lose hot water immediately. – mike65535 Jan 14 '19 at 16:32
  • @Machavity Yes, turning it back on immediately restored cold water. – VivaLebowski Jan 14 '19 at 16:48
  • @isherwood Added pictures! And also, isn't it hard enough posting for the first time on a new StackExchange site without this semantic nit picking!!! ;) – VivaLebowski Jan 14 '19 at 17:12
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    I think the word you're looking for is "pedantic". :D :D Apparently you did turn off the correct valve and this is quite a mystery. – isherwood Jan 14 '19 at 17:23
  • @isherwood It is indeed! To quote Zoolander, I feel like I am taking crazy pills. Will inspect more later and get back to this post with updates if no answer is forthcoming :/ – VivaLebowski Jan 14 '19 at 17:33
  • Is that valve above the wh the only valve that was shut off.? – Kris Jan 14 '19 at 17:46
  • @Kris Yes; the only other thing I did after we spotted the leak was flip the circuit breaker to off for the water heater. – VivaLebowski Jan 14 '19 at 17:49
  • https://terrylove.com/forums/index.php?threads/no-cold-water-when-water-heater-shut-off.56970/. I thought this thread had the answer but if your toilets quit getting cold water I’m lost – Kris Jan 14 '19 at 18:03
  • Do you have a mixing valve in your shower plumbing? Were you using your clothes washer when the cold water failed? – A. I. Breveleri Jan 14 '19 at 19:07
  • That is really strange, did you drain the water heater? Even with it drained the toilet should fill, I was thinking if the drain was open when a single handle faucet could allow some of the water to flush back through but there would still be some water at the sink and the toilets should not have been affected. – Ed Beal Jan 14 '19 at 19:08
  • Are your water supply lines the type called "flood safe"? Did the cold water tap in the shower continue to deliver cold water when the other ones did not? – Jim Stewart Jan 14 '19 at 23:34
  • @mike65535 it really depends on the system, when I was remodelling in my house with my father, when turning off the main water intake and the hot water heater, the cold water stopped directly, while the hot water flowed for some time – Ferrybig Jan 17 '19 at 17:01
  • @Ferrybig Sounds like you had a pressure tank between where you turned off the cold water and where the cold water enters the water heater – mike65535 Jan 17 '19 at 17:05
  • Did you figure this mystery out? – Kris Jan 18 '19 at 03:27
  • @Kris Sadly no, but that's more due to not having time during the work week. We turned everything back on and are just carefully watching the leak while we arrange for a replacement heater to be installed. Will probably try to recreate this mystery tomorrow or Sunday! – VivaLebowski Jan 18 '19 at 14:37
  • @VivaLebowski Did you ever figure this out? – UnhandledExcepSean Jun 13 '19 at 13:13
  • @UnhandledExcepSean No, in the business of getting it replaced I didn't have time to properly diagnose; we got it replaced with a new unit, so I suppose this post should be deleted since we never found an answer... – VivaLebowski Jun 13 '19 at 20:59

2 Answers2

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If that is truly the case as you reported it, something is seriously wrong with the design of your plumbing system and you are mixing hot and cold water all of the time, which would be costing you a fortune in electricity bills.

Are you sure it was ALL of the cold water lines that were off? On things like showers, bath faucets and in some places, sinks, there is an anti-scalding / temperature balance valve used to mix cold and hot automatically. With no hot water at all, it may have interpreted that as there being too much cold water, so it kept reducing the cold water in an attempt to balance the temperature. But that would typically not be associated with your toilets. MAYBE, if you are in an extreme environment where the toilets might freeze, someone did that to put a little warm water into the toilets too, but I have never seen that.

JRaef
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  • Just thought of something: if the hot water pipes were run right next to the cold water pipes in an outside wall, the loss of hot water may have allowed the cold water pipes to freeze! That would explain why it took a day to take effect. – JRaef Jan 14 '19 at 22:19
  • Except when we turned the cold water valve to the heater back on, cold water flow was restored immediately. Our townhouse has two houses on either side and we haven't experienced any freezing issues yet, so I don't think that's an issue. I haven't had time to make an exhaustive investigation since yesterday :/ – VivaLebowski Jan 15 '19 at 15:02
  • @VivaLebowski Sounds like you had a pressure tank between where you turned off the cold water and where the cold water enters the water heater. I'm only aware of pressure tanks being on well systems, but perhaps you have something performing that function? – mike65535 Jan 17 '19 at 17:08
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    @mike65535 I added pictures in the post above; don't think that's it. We have a normal setup to the best of my knowledge. There is absolutely nothing but copper pipe between the valve I turned and where it enters the top of the water heater. – VivaLebowski Jan 17 '19 at 17:56
  • The first home I owned had a mixer valve going to the tank as an anti-sweat feature for hot weather. – GOATNine Mar 29 '23 at 14:49
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Maybe your shut off valve is before your other lines therefore shutting off all the the water.my pipe from the meter runs directly to my water heater with lines branching off above it. So if they put the shut-off valve before those branching lines that would stop water flow throughout

Brian
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