Navien NPE-240A Trouble

Discussion in 'Tankless Water Heater Forum' started by dsnow0819, Mar 13, 2019.

  1. dsnow0819

    dsnow0819 New Member

    Joined:
    Mar 13, 2019
    Location:
    MS
    Hello, I'm hoping someone can help with my water heater problem.

    Hot water runs out in the shower and faucet. Doesn't go completely cold but not even luke warm after a few minutes. If you are taking a shower and turn the water off for a few seconds then back on the hot water will come back but run out agin. I can also hear a loud moan/groan noise from the unit/pipes as it is right above my master shower. Water out of the faucet does the same thing.

    Steps taken: cleaned the air intake filter, cold water inlet filter, recirculation filter and condensate clean out. None were extremely dirty but had some minor build up. I also drained the unit and the water was pretty brown.

    Readings and other items: well water, unit is about 2.5 years ago, natural gas, no problems before, set to 125 degrees , GPM with faucet on is 0.4-0.6, shower is 0.8, water temp drops when shower is turned on but recovers to 125.

    Called navien support and they said all the readings were normal but the GPM was low.

    Any ideas?
     
  2. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Water hardness can lime up the heat exchanger in the unit in as little as 2 years, reducing it's flow, increasing the pressure drop across the tankless at flow. With big pressure drops on the tankless some shower mixers and anti-scald valves stop doing the right thing, often restricting flow on the hot side more than it should. This is a common issue with tankless water heaters on wells, unless there is a functioning water softening treatment system ahead of the water heater.

    The higher the water temperature, the more rapidly lime deposits can form. Is there any reason for running it at 125F? Most house can do just fine with 115F water entering the hot water distribution plumbing. A tub fill is typically ~110F, a shower typically ~105F, give or take.

    De-liming the water heater with a small pump recirculating vinegar through the unit for an hour or so may improve the flow and make the symptoms go away.

    Low water pressure can also make tankless water heaters mis-behave. The minimum specified operating pressure for the NPE-240A is 15 psi or better (measured at the tankless). See page 6 of the manual. I'm not sure what the absolute minimum pressure it will operate at before it shuts down and spits a code, but it's probably at a pressure lower than 15psi, and it could induce symptoms that make noise from "kettling" of flash-boil at low flow across the heat exchanger.

    Check the pressure, then lower the output temp to 115F, see it it behaves any better.
     
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  4. dsnow0819

    dsnow0819 New Member

    Joined:
    Mar 13, 2019
    Location:
    MS
    Thanks for the reply. The temp was set at 125 by the builder and I honestly never changed it.

    I'm assuming its calcium because our water is terrible. Killed my ice maker in under a year before I put an inline filter on it.

    Two last questions and I really appreciate the help.

    First, how do I check the pressure? Can the navien unit?

    Also, can I put an inline filter on the cold water in to help if the build up is the problem?

    Edited: Check that last question. Seems like I need to put a filter on it.
     
    Last edited: Mar 13, 2019
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    I'm not sure if that water heater can report a water pressure (read the manual!) A cheap hose-bib type water pressure meter can work. If there isn't one close to the water heater, run a hose to the water heater from a hose bib with the meter on the end of the hose. That will at least give you the static pressure (but not the pressure drops from the plumbing when water is flowing.) If it's 15psi static pressure it's too low, but 25psi or higher should be adequate. With well systems the storage tank pressure is always adjustable.

    Certainly filtering the cold water doesn't hurt, but a water softener &/or periodic de-liming is really the best solution. Many installers will install isolation valves and ports to make de-liming easier when installed on a hard-water system.

    There are dozens of online videos on how do de-lime these things. As a first shot try using white vinegar for the rinsing agent, nothing stronger.
     
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