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Shower pressure drops

I have two showers in my house. **ALL heat and hot domestic water is provided by oil fired boiler** Only one shower can be used at a time or the pressure drops to a trickle. In fact if one is in use and hot water is turned ANYWHERE else in the house the same thing happens. There is a mixing valve in the system as well as a circ pump. Finally, the overalll pressure is slighter better in cold supply than hot water. Any ideas?


  • Jamie Hall
    Jamie Hall Member Posts: 23,443
    Well, the common factor is the mixing valve. So I'd start looking at it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,261
    Check for plugged screens on the valves. Pressure reducing valves in the main water supply are a place to check, as well as the mixing valves

    Mix valves could have a screen on hot and cold ports

    A shut off valve that is not fully opened could be a cause also
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • PRR
    PRR Member Posts: 156
    edited January 2020
    > the overalll pressure is slighter better in cold supply than hot water.

    Flow pressure is normally lower on hot because of the drag in the water heater.

    Was it always like this or has it been going down for a while? If a screen fills-up slowly, you don't notice at first, but comes a day when ANY other load makes an intolerable drop.
    Had a truck that would cruise to Maine but coffed on long hills. Had a brain-tickle. Blew out the fuel filter. Crud! With maybe 20% open area, it would cruise but not pull a hill. Had been driving the flatlands fine.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,806
    What kind of water heater , are you using the boiler coil pumping into a storage tank or is it piped as a extra zone piped to a tank . I am assuming you have a storage tank as you mentioned a circulator .If off the coil is there a check valve directing the incoming cold water though the coil ????

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