I am not a plumber.

When I close the hotwater outtake valve from the hot water cylinder, I had expected that hot water water would stop flowing from the hot taps/faucets. i.e I expected no water.

However, cold water flows instead from the hot tap. If I open the hot water line valve, then hot water again flows from the hot tap.

Does this indicate a problem somewhere or is that expected behaviour? If it is a problem - is it one that should be addressed or can it be safely ignored? This is a rental property where the landlord strongly desires to repair nothing.

I have recently installed a washing machine, never made the above test prior to installation so unsure of relevance.

1 Answer 1


The mixing valve of the washing machine can let cold water into the hot line. Also single valve lavatories and kitchen faucets. You can tell which one is allowing the flow by turning off the cut-off valve to that point of use.


This is only occurring when the hot water line is shut off. It is not a fault condition. It happens all the time with the single handle sink mixing valves.

  • Same would be true if the OP has an instant hot water system.
    – BillDOe
    Apr 3, 2017 at 1:36
  • Is it a considerable problem if cold water is let into hot water line? Hot water tank works fine, and power bill seems reasonable.
    – Mtl Dev
    Apr 3, 2017 at 3:49
  • It is not a problem because it will not occur when the hot water cut-off is open, i.e., in normal use. It is only occurring when you have the hot shut off and there is no pressure in the hot line. Why did you shut off the hot water supply? Are you doing this regularly for some reason or just to do a repair? Apr 3, 2017 at 10:37

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