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NAVIEN NPE-240A temperature fluctuation

mrbill15 Member Posts: 1
When taking a shower, the temperature fluctuates. I've done two things that can stop this.
1. Remove the front cover and let the unit run, or
2. Detach the PVC pipe from the inlet air. [Note, I have confirmed that there is zero blockage in the inlet air pipe or filter.] [I have not done anything to the exhaust side, though I know the exhaust PVC pipe does get warm when the unit is heating.]

Is it possible that there is an internal exhaust leak, causing back pressure and less than adequate inlet flow? The pressure goes away when either steps 1 or 2 above is done. Also, there is a fair amount of the dark oily buildup on the bottom of the heat exchanger which I've read could be related to exhaust.

Thanks for your help!


  • hot_rod
    hot_rod Member Posts: 22,251
    Is there a flow restrictor in the shower head? It may not be flowing enough gpm to keep the burner firing, so it is on and off a lot

    what about running a different hw fixture, a tub filler maybe, see how it performs 
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GroundUp
    GroundUp Member Posts: 1,924
    Is there a mixing valve installed? Neither of the things you mentioned should have any bearing whatsoever on the issue at hand. 99% chance it's related to flow, and if there's no mixing valve, it's because the flow rate is falling between modulation rates like @hot_rod mentioned above.
    EBEBRATT-Ed Member Posts: 15,607
    Look at some U tube videos. Navien's have a problem with a leaky flue gasket that deteriorates (the oily stuff) and it causes recirculation of the flue gas.
  • SuperTech
    SuperTech Member Posts: 2,183
    The brown oily residue is an indication of flue gas leakage from the heat exchanger or flue gas recirculation from the intake pulling exhaust back in because they are too close to each other. I would take a good look at how your intake and exhaust are installed in comparison to what the installation manual shows.  What you are experiencing is fairly common with Navien units, even when the venting is done correctly. 

    I believe the YouTube videos were pulled since the class action lawsuit started.
  • pedmec
    pedmec Member Posts: 987
    You can watch the flow rate by pressing the information button. it will also give you the return and supply temps by press the down button. The 240A has a recirc pump built in and sometimes the check valve will fail and you will get a cross connection in the water heater. you can shut the flow off by moving the handle on the left of the recirc