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Locknivar NKC199N Combi boiler steady dripping from pressure outlet pipe

dseltzdseltz Member Posts: 14
My Locknivar noble nkc 199 boiler is steadily leaking from pressure outlet pipe. Pressure looks low though (10psi). Any ides what could be going wrong?


  • STEVEusaPASTEVEusaPA Member Posts: 4,192
    Has it released recently?
    Double check pressure with a known proper working pressure gauge.
    If pressure is good, you'll have to replace it.
  • JUGHNEJUGHNE Member Posts: 6,962
    Your expansion tank could also be waterlogged.
    Just depress the tank schrader valve, maybe under a blue cap, just for a split second. Do you get air or water?
  • dseltzdseltz Member Posts: 14
    Well after overflowing a bucked overnight and then filled up half a bucket in about 3 hours but now it has stopped. Pressure value still says ~ 10 psi. What do you mean “has it released recently”? Don’t see a Schroeder valve on my expansion tank.

    We do have hard water here by the way.
  • JUGHNEJUGHNE Member Posts: 6,962
    The Schroeder valve should be on the bottom.
    I see you are fortunate to have an isolation valve above the tank.
    If you shut off the boiler, shut off the cold water supply, close that isolation valve and unscrew the tank just enough to release any water pressure in it.
    The tank should then feel empty, if not when removed it needs replaced.
    To sum it up: with the tank disconnected, laying on the floor it should have 12-15 PSI of air in it. If water logged it is heavier than you imagine. Don't damage the Schroeder valve.
  • dseltzdseltz Member Posts: 14
    OK, got it. Thanks. Right now the dripping is still stopped. If it starts again I’ll follow your steps. Thanks!
  • JUGHNEJUGHNE Member Posts: 6,962
    You may need more than that 10PSI (if correct) for your system to operate correctly.
    Some service people will never test/flush your pop off valve for fear of it not reseating and dribbling forever.

    I test all I come across at least once a year. Lift the lever and let it run for a couple of gallons. You may get a shot of nasty looking water with the first operation. Then snap it shut hard to make sure it is reseated and not leaking. This also tests the refill valve to bring the pressure back up as needed.

    Of course I have a spare close at hand.
    If done every year then this keeps the seat clear and seldom do you have to replace them.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,079

    If you isolate and unscrew the expansion tank be careful. If the tank is light it is probably be ok.. If the tank is defective it could be waterlogged and could be full of water and will be broken toes!!!!
  • IronmanIronman Member Posts: 5,673
    If that's a combi, there are two separate relief valves: one on the boiler side and one on the domestic side. To which one are you referring?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • bob eckbob eck Member Posts: 915
    Noble combi boiler comes with a 50 PSI yes I said 50 PSI boiler relief valve from the factory all three size BTU inputs of 110K, 150K and 199K. Check the tag on your boiler relief valve. Is it a 50 PSI boiler relief valve. The installing contractor could have switched the 50 PSI relief valve for a 30 PSI boiler relief valve that is the normal PSI on most residential boilers in America.
    We have been selling the Noble combi boiler since they came out and I told my Lochinvar rep BJ Terroni to ask Lochinvar if they could put a red sticker on the side of the combi boiler near where the relief valve is mounted so contractor notice the relief valve needs to be 50 PSI. As far as I know Lochinvar has not put a sticker on the combi boiler saying 50 PSI boiler relief valve needed.
  • dseltzdseltz Member Posts: 14
    Ok, so this leaking from the pressure outlet is happening again. Just overflowed one bucket. The unit does have two release valves, on one top and one on the bottom. The one on top does say 50 psi. The pressure valve says about 25-30 psi. We did lose power lately and I notice the 3 zone switching relay has a red light for zone three.

  • Jamie HallJamie Hall Member Posts: 12,943
    We still don't know which relief valve is dripping. Please...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • dseltzdseltz Member Posts: 14
    It is not coming from the boiler relief valve on top of the unit. The pipe you see dripping in the picture is connected to the Boiler side (and to DHW in). Here is a better picture:

    Note if I quickly press the schrader valve on the expansion tank (in the picture) I get air not water).
  • dseltzdseltz Member Posts: 14
  • ZmanZman Member Posts: 5,865
    It looks like the water is coming from the vent on the backflow preventor. Is the water to the valve turned on?
    @Hotrod knows a great deal about that device :)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • dseltzdseltz Member Posts: 14
    Yes I believe the water is on. The boiler seems to be running fine besides the dripping. it's still going.
  • ZmanZman Member Posts: 5,865
    In my experience, they drip when the supply water is off and they drip when debris gets in the inner workings. Replacing it would be the easiest path.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • dseltzdseltz Member Posts: 14
    Ok, thanks Zman.
  • hot_rodhot_rod Member Posts: 13,457
    probably just some debris in that Dual Check back flow preventer. Fairly easy to disassemble with na vice and large Channelock pliers. Dirt or teflon tape under one of the O-ring seals.

    Most installers just replace them :)

    The seals under those cone shaped valves is where you will find the debris.

    Do the boiler have a low water cutoff safety, looks like one in the pic? If so you could just shut off the fill valve.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • fenkelfenkel Member Posts: 81
    Check the o-rings for small rips or tears, we have seen a few that will leak consistently if there're damaged...
    Fyi: we starting up the system... turn the water to that device on slowly, sometimes a pressure change can cause that relieve valve/ seal to open and close too quickly and cause it to rip...
    In our area, we can not use these, we need to use rpz styled back flow preventers on make up water..
    For indirect and combi boiler install, we'll use a spring or swing check valve in place of the backflow preventer, we then will add a expension tank in line after it to the indirect or combi water heater...
    I think ( not sure) the lockinvar noble combi boiler manual shows the install this way...
  • dseltzdseltz Member Posts: 14
    Just to close the loop the problem was the backflow preventer which I've replaced. Thanks for all the help.
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