Water coming from hot supply line after valve supplying shut off

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Old 12-17-16, 10:40 AM
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Water coming from hot supply line after valve supplying shut off

I removed my water heater to repair a leaking pipe. I shut off the valve coming from the cold water supply to the water heater. Drained the water heater, then proceeded to cut out a section of pipe that needed to be removed for repair. Some water began to leak after breaching the pipe. I assumed it was water still in the lines above (second floor). However, someone in the house used cold water for something, then water began to FLOW! I shut off all the water to the house and the water stopped. Why is there water coming out of my hot pipe when I have the valve supplying the water heater shut off?
 
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Old 12-17-16, 10:46 AM
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I'm not a plumber, so I'm just guessing. because we have sinks with a single knob to adjust waster? If someone doesn't have a knob turned all the way to cold, is water going from the cold line down through the hot? Sounds like a stretch, but I don't know how else the cold water is getting in to my hot line.
 
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Old 12-17-16, 12:05 PM
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Yes, water can back flow through a faucet if someone turned it on.
 
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Old 12-17-16, 12:23 PM
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Thank you, Pilot Dane.>>>>>>>>>>
 
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Old 12-18-16, 08:19 AM
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That person that turned on the cold water must also have turned on the hot water as well. Traditionally the water pressure from the hot water side would prevent the backflow, but without pressure the cold water will flow into the hot side as easily as it will flow out the faucet spout.

As far as the water is concerned, your cut pipe is just another spout for it to flow out of.
 
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Old 12-18-16, 01:57 PM
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If you didn't vent all the hot water valves above the the tubing being cut, a vacuum lock can occur in the tubing at any applicable hot water valves which prevents the water in the tubing from draining by gravity. If someone opens that hot water valve. the vacuum is exposed to atmospheric pressure and the water in that tubing will flow out the lowest open part of the tubing (you get a shower). This assumes all tubing is sloped properly. Good luck
 
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