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Thread: tankless-luke warm shower

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  1. #1

    Default tankless-luke warm shower

    I recently installed a tankless hot water heater. I have a shower panel with a single handle adjustment with a mixing valve. The only way I can get the shower hot is by restricting flow at the gate valve on the cold supply line. I have adjusted the shower anti scald valve all the way to its hottest setting. All other fixtures in house will produce hot water. I did notice in a second bathroom that has an older valve setup that when only the hot water is turned on all the way that the flow is not as strong as it used to be prior to hooking up the tankless unit. It does come out hot but the flow rate is less than if you turn on only the cold side. Could the imbalance in flow rate at the mixing valve be the reason for not getting a hot shower? Can I put a circulation pump on the hot line to increase the pressure to match that of the cold line? Do I put the pump after the tankless unit or before it? Thanks for your help.

    Water pipe sizing
    Last edited by Terry; 02-08-2009 at 08:37 AM.

  2. #2
    Master Plumber Dunbar Plumbing's Avatar
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    Sounds like an undersized unit.

    No fixes for that.


    You're exceeding the demand that tankless will provide.



    Use a water saver showerhead.


    Did you buy the bosch from lowe's/home depot?
    Read what the end of this sentence means.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Almost all tankless systems have a flow restrictor in them. So, not seeing as much volume in the hot side verses the unrestricted cold side is entirely normal. I do not know for sure, but wouldn't be surprised that the valve will not allow all hot input, and because the cold is full flow, you may never get hot enough. The pressure balance function may be restricting the hot flow.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4

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    To get an informed answer first make sure that your heater is perfoming right.


    1. Measure the temperature of the hot water at the sink closest to the shower after the hot water has run for a while.

    2. Measure the temperature of the cold water at the sink closest to the shower after the cold water has run for a while.

    3. Measure how many gallons per minute you get from your shower head with your normal settings.


    The make and model number and type (gas/electric) of the tankless is also needed.

  5. #5
    Master Plumber nhmaster's Avatar
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    Ain't tankless heaters great? Note the number of threads about tankless problems compared to threads about tank water heater problems.

  6. #6
    In the Trades Gary Swart's Avatar
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    I wondered how long you could keep quite on this one. Gotta love tankless. Without them and Whirlpool WHs it would be lonesome.

  7. #7
    Master Plumber nhmaster's Avatar
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    I had a nightmare last night. House piped in CPV and ABS with a tankless water heater, Champion toilets and Moen valves throughout. AHHHHHHHHHHH.

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