Plumbing – Water began flowing from some taps even with whole house shut off

plumbingshutoff

I recently shut off the whole-house water supply when replacing 2nd floor bathroom sink faucet cartridges because I couldn't get the sink supply line shut off all the way for the hot side to close all the way. I opened the other bathroom sink taps to verify water was truly off and started working.

After maybe an hour, maybe a bit less, water started coming from the open taps of the second sink (which were open), and dripping from the showerhead (which was not). No water came from the faucet on which I was working – though I also had the under sink shutoffs shut.

Why did this happen? Did I just not have the whole-house valve shut all the way? If so, why the delay? Was water just slowly making its way to the 2nd floor? Is there something else going on here that I'm overlooking, like, should have also turned off the supply just to the hot water heater (though the whole-house I thought would trump that)?

All ended up fine, but I'm interested in any ideas why this would have happened.

Thanks,

Andrew B.

Best Answer

Okay, we gained more info in the comments, and now the order of events seems clear:

  1. You turned off the water to the whole house,
  2. opened taps on the first floor AND second floor to drain the pipes
  3. closed taps on the first floor and then went to work
  4. after about an hour, the taps on the second floor start to drip

We can now see the reason for the delay: Clearly the 'whole house shutoff' was not completely closed, and the water had to slowly fill all the pipes up to the level of the second floor. If you had left a tap open on the first floor, you would have seen the drip almost immediately.

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