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Navien NPE-240A losing heat

StanS
StanS Member Posts: 2
in Domestic Hot Water
I've got a Navien NG that's about 10 years old. When I first turn on hot water, it heats up but then gradually drops the temperature to about 100 (set to 120 or 125, doesn't matter). If I add GPM by opening the tub, it gets to 118 and stays.

I've descaled it and replaced the flow sensor, no change. Had a contractor out, he didn't have good ideas. It looked like condensation inside, but I think it's spraying from the recirculator pump's red cap when it was being flushed.

Here's video of out temp from the unit: https://photos.app.goo.gl/uvBFVz3Tng5uXmMJ7

Hope someone has ideas. Thanks!

Comments

  • pedmec
    pedmec Member Posts: 1,026
    you need to go into the service menu

    press the wrench button

    the menu starts at:
    A) flow rate/ gpm's. write it down.
    scroll down to
    B) Hot water out
    scroll down to:
    C) cold water in

    subtract B-C= X

    multiply X/500/gpm= BTU output

    scroll down to D to see if the capacity is close to the BTU output

    This just to start. To see if its matching. If its matching then you need to confirm the numbers that the control sensors are seeing by using a thermometer. it will be firing at a rate that the sensors are telling it.
  • StanS
    StanS Member Posts: 2

    Following up on this. On someone's advice, I turned off the valve to the recirculation pump and now it works fine. The problem seems to be a leaky valve between recirculation pump and the intake, which lets cold water from supply get into output without going through the pump. I haven't replaced it but seems like the only thing it could be. Thanks for the help!

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