Navien NR-240 Pressure Relief Vave Spraying

Discussion in 'Tankless Water Heater Forum' started by William Cutrone, Mar 16, 2019.

  1. William Cutrone

    William Cutrone New Member

    Joined:
    Mar 16, 2019
    Location:
    Staten Island
    Hi, my 7 yr old Navien tankless water heater has been intermittently spraying water from pressure relief valve every day or so.
    I changed the relief valve and it still happens.
    The manufacturer said to check my water pressure.
    I am currently monitoring my water pressure for my house with a pressure gauge. My incoming water pressure is roughly 50psi. I did see 1 high reading with the red dial on the gauge of roughly 150 psi. Could I really have a surge that high?
    The red dial on pressure gauge seems to jump when I shut the water. Could I be experiencing a “water hammer”?
    Also I’ve been monitoring water pressure and it seems to spike at certain times. For instance, I had a reading of 120psi and a high of 140. This doesn’t seem right
     
    Last edited: Mar 17, 2019
  2. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Yes, water hammer spikes with rapid turn-off can easily exceed 150 psi on a static 50 psi system.

    If your static pressures are sometimes hitting north of 120 psi it's time to install a pressure reducing valve. The max rated pressure for most Naviens is 150psi, but it doesn't take anywhere near that to push a lot of flow through the tankless. Regulating it to no more than 80psi (the pressure at which showerheads are flow-rated) or even 50 psi is fine.
     
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  4. William Cutrone

    William Cutrone New Member

    Joined:
    Mar 16, 2019
    Location:
    Staten Island
    Thank you for the reply. Yes I will be installing a PRV this weekend. I’m surprised more people haven’t posted about this issue. The DEP told me since the water in my area is pumped to me it can cause higher pressure during off hours. Such as what I am experiencing now, static pressure of 120-130 during off hours. Because my tankless doesn’t require an expansion tank, the pressure relief valve is opening. I hope this thread helps other people with a similar problem
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    If you see 100 plus pressure, but that pressure drops below 80 when you dribble just a little water from a faucet, you don't need a PRV. Instead I would then think you need a thermal expansion tank, despite supposedly not needing one. My comments are not based on experience.
     
  6. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    That would only be true if there were a check valve or pressure reducing valve already in place. If the water can flow both directions through the meter the local water system is the expansion tank.

    With a tankless as the only water heater it isn't usually necessary to have an expansion tank. With a tank type water heater PLUS a pressure reducing valve an expansion tank is a good idea.
     
  7. William Cutrone

    William Cutrone New Member

    Joined:
    Mar 16, 2019
    Location:
    Staten Island
    Update:
    I installed the Pressure reducing valve today on my water main coming in. However, after using tankless water heater my relief valve sprayed again and both my pressure gauges (up & downstream)were at roughly 140psi. So I believe the pressure reducing valve is acting as a check valve and not allowing the thermal expansion to return into the city water.
    I figured I’d need a thermal exp tank no matter what and now I’m convinced I need a thermal expansion tank?
    If so, do I install it on cold water line before it enters tankless. Also, is a 2 gallon expansion tank the right size.
    I attached a photo of the PRV I installed today.

    Side note: when water pressure was @140psi, as soon as I opened my faucet it dropped instantly back to 50psi. According to instructions for PRV that’s a sure sign of thermal expansion
    5DC22F12-F29B-4281-B347-E07A1676AA38.jpeg Thank you
     
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