Pressure Balance for "on demand" water heater

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by hopkinsck, May 20, 2005.

  1. hopkinsck

    hopkinsck New Member

    May 20, 2005
    I recently installed a Bosch AquaStar 250SX on demand hot water heater. Since the installation, I've had problems with temperature cycling in the showers when someone else in the house is using water. The user manual suggests that unbalanced water pressure and the hot water heater restricting flow could be resulting in the hot water flow dropping below the .8 gal/min flow required to activate heating. Is there a water pressure balancing valve that would be appropriate to install immediately downstream from the hot water heater? If I do this, is it likely to solve the problem? By the way, the incoming water pressure to the house is 80 PSI, and I see 80 PSI far downstream on the cold water side. I don't have a place to measure the hot water side.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Tankless waterheaters output water temperature can vary quite a bit with changes in volume. I'm not sure what you are seeing is not normal for that type of install. They work much better when you are the only user. My unprofessional opinion.
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    water flow

    What is more likely is that when someone else uses water it is either exceeding the capacity of the heater resulting in a loss of water temperature, or the flow rate increases so that the pressure drop through the heater is "huge" resulting in the cold water pressure overpowering the reduced hot pressure. A pressure balancing shower valve, or a pressure balancing valve ahead of the shower may be the only ways to solve your problem.
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