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Pressure Drop

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  • Pressure Drop

    I have what seems to me as an interesting question.

    In my shower the hot pressure is poor. All other faucets seem fine.

    When the shower is on, and someone turns on the hot water in the bathroom sink, shower water slows to a trickle but remains hot. BUT if you turn on the cold water in the sink at the same time the hot is on, the pressure in shower actually increases beyond the “normal” pressure when sink is off. ..but shower gets cold. Shower pressure does not decrease if just the cold is on.


    Why would pressure drop when hot is turned on and not cold? Why would the pressure increase when both hot and cold are turned on ? Why would shower get cold when cold water turned on in sink?

    I share this bathroom with three others and it is rather irritating. Pressure/temp not affected by any other situations.

    I live in a three unit rental and to my knowledge the building uses boiler for both heat and water.

  • #2
    Re: Pressure Drop

    You have a pressure balanced shower valve, and it is responding to changes in pressure on your hot or cold lines. I would not expect the pressure to vary so much, so perhaps the pipes in your building are too small, or plumbed "funny".


    • #3
      Re: Pressure Drop

      The problem is an obstruction somewhere in your hot water line before the connection where the sink/shower tee is. Possibly a partially closed valve, etc. When you turn the hot and cold water on in the sink, the cold water is actually backfeeding from the sink faucet to the shower, creating the increased pressure and the drop in temperature. I would guess that you are either dealing with galvanized piping at some point or there is a valve that is obstructed/partially closed.
      Once you become a pickle you can't go back to being a cucumber.


      • #4
        Re: Pressure Drop

        ....And the problem with the old galvanized piping is it's old,scaled/rusted up.( equals poor pressure esp. with the cold side.)
        We are somewhat assuming you are talking about an older building and this is an ongoing problem.


        • #5
          Re: Pressure Drop

          Devine is spot on! The low of hot water from the basin is sufficient to meet your needs, but not so in the shower. Chances are, the piping from the sink to the shower is halfway decent. If you run a hot water line from a good flowing bathroom to this bathroom you may solve this problem rather inexpensivly.