Rinnai Bath Fill Mode with Shower Mixing Valve?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Chins, Mar 23, 2014.

  1. Chins

    Chins New Member

    Messages:
    10
    Location:
    CA
    Hi All,
    I am looking at purchasing a tankless hot water heater and the Rinnai I am thinking of has a remote with a bath fill feature. Basically, you tell it how many gallons of hot water you want and the temperature you would like it and it will fill the bath with the specified volume of hot water at the specified temperature and then turn off. So in theory you can walk away while the tub fills up.
    Easy enough if I had a separate faucet for hot and cold water. However, I have a shower mixing valve so I was wondering if I adjust the mixing valve to maximize the hot water and then turn the mixing valve to full hot will I get the same result? I figure that the water volume and temperature would work but would when the water heater stops the flow of the hot water would the water stop at the mixing valve to or would I just get cold water coming out?
  2. Terry

    Terry Administrator Staff Member

    Messages:
    14,889
    Location:
    Bothell, Washington
    That depends on the settings on your valve. With a temperature stop, at the high setting it may be a hot/cold mix.
  3. Chins

    Chins New Member

    Messages:
    10
    Location:
    CA
    Thanks Terry. So if the valve didn't have temperature stop then it would work? Is there such a valve?
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,487
    Location:
    Cave Creek, Arizona
    The majority of "shower" valves have a pressure balancing module inside them. IF the heater turns the hot water flow off, i.e., zero pressure, the module will also turn the cold to zero pressure, effectively turning it off also.
  5. Chins

    Chins New Member

    Messages:
    10
    Location:
    CA
    Thanks, I guess I will give it a try after the install and see what happens.
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