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Problems with lochinvar noble combi nkc110

I have 2 issues with my boiler installed almost 5 years ago and has never worked right.
1) inlet temperature sensor has always read 2 degrees below outlet temperature even when I can feel a very obvious larger difference by touch and by infrared thermometer. If the sensor is faulty, shouldn’t it not consistently read close to outlet temperature? I would like to check the resistance of this sensor but is it in direct contact with water or is it inside a chamber? I don’t want to drain the boiler just for this. Does the inlet temperature even affect how the boiler functions?

2) This one is complicated. I have 2 zones. When each is open on their own, the boiler works great. But when they are both open at the same time, some of the system return water goes back into the system instead of to the boiler. This cools the water so the system sensor continues to call for more heat so that the boiler ends up heating up to 30 degrees higher than the system temperature. When it is particularly cold ( I live in the northeast), my boiler frequently hits max temp and slows down. I can never get 180 degree water entering the system.
The problem is exaggerated when I increase the speed of my system pump so I have to keep it at the lowest speed.
My boiler was repiped to shorten the distance between the system send pipe and the return pipe but this did not solve the problem. The boiler pump was replaced with the same pump but did not help. Would a stronger boiler pump overcome this “path of least resistance” when both zones are open? I currently have grundfos UP 15-78 cil2 60 hz 130w.

Attachment shows both problems.


Comments

  • neilc
    neilc Member Posts: 2,087
    people will want to see how this is piped,
    1 or 2 distant shots showing everything, circs, valves, piping and connections to boiler, all in one shot
    known to beat dead horses
    HomerJSmith
  • gloria
    gloria Member Posts: 11


  • gloria
    gloria Member Posts: 11
    Let me know if there are any other photos I should post. Thanks!
  • neilc
    neilc Member Posts: 2,087
    the circ in the picture,
    is it pumping up, or down?
    from here I think it's pumping down,
    and that might be backwards,
    could you post a close up of the pump label over to the insulated sensor to the right,
    and a second of the circ from the side or behind so the circ velutes can be seen,
    is there a directional arrow on there somewhere?

    what model boiler?
    is the inlet the right or the left under there?

    boiler water is flying around the boiler loop,
    we need to figure why the system isn't drawing it,
    known to beat dead horses
  • neilc
    neilc Member Posts: 2,087
    neilc said:


    what model boiler?

    got it , , ,
    "lochinvar noble combi nkc110"
    known to beat dead horses
  • hot_rod
    hot_rod Member Posts: 18,210
    Is the system pump running delta T mode?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • gloria
    gloria Member Posts: 11
    Inlet is on the right in the photo.
    System pump is at the lowest constant speed…any higher and it draws more water from the return pipe.
    As I said initially, the inlet temp reading is wrong and always has been. I have confirmed this with an infrared thermometer. So we can’t use this to determine water flow. All I can confirm is that too much return water is going back into circulation and not back to the boiler. The path of least resistance for some of the return water when both zones are open seems to be through the system loop and not
    back to the boiler.
    As far as I can tell the system pump is installed correctly and pumping the water in the correct direction.



  • gloria
    gloria Member Posts: 11
    I can’t get a photo from the other side of the pump but I can feel the arrow indicating the direction of flow and it points upwards so it is installed correctly.
  • hot_rod
    hot_rod Member Posts: 18,210

    Sounds like it is not getting adequate flow. Any strainers added in the piping. Could be the shuttle valve on the DHW module. That pump should be plenty for the loop you have

    Test the sensors by removing the plug on the sensor, or at the other end where they connect to the circuit board. The sensors screw in, so somehow the wires remove from it.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Le John
    Le John Member Posts: 211
    try lowering the MAX SH SETPT temperature and raise the SH SETPT (COLD DAY) temperature – found in Set Points Menu.
  • gloria
    gloria Member Posts: 11
    My question, as above, is this: is the inlet sensor probe in a chamber devoid of water or does it insert directly into the water flow? If it is directly into the water flow, then I would need to drain the boiler to remove it. I did try to unscrew it but water started coming out so I assumed it was in the water flow. Does anyone know?
  • gloria
    gloria Member Posts: 11
    There are no strainers and the check valve originally installed was removed in case it was impeding flow. How do I check the shuttle valve? It certainly seems to be functioning properly. I get hot water with no problem and can hear it click when the hot water is being called.
  • hot_rod
    hot_rod Member Posts: 18,210
    I had that boiler in my last home, as I recall the sensors screw into the piping near the boiler, so you would need to drain to replace. But they can be checked without removing them. Disconnect the plug and attach an Ohm meter.
    Does the boiler short cycle, on off frequently? That can cause them to overshoot a bit.

    The system pump should run when the boiler runs to move the heat around. If just the boiler runs it can run up over temperature also, no place for the heat to go, so supply and return temperatures get close like you show.

    A point and shoot temperature gauge or a strap on type gauge would give you some actual temperatures. In an out of the boiler and supply and return to the system.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • gloria
    gloria Member Posts: 11
    I appreciate everyone’s help.
    I have used an infrared thermometer to check temperatures. The inlet temperature probe is definitely wrong.
    I have the curve set up so that short cycling rarely occurs, especially in the winter.
  • gloria
    gloria Member Posts: 11
    Also if you look at my very first photo, both pumps are running and the inlet still shows similar temp to outlet. So that’s not the issue.
  • gloria
    gloria Member Posts: 11
    Thank you hot_rod for stating the obvious about measuring the resistance of the probe without removing it first. Duh. But anyway, using my thermometer and measuring the resistance definitely shows the probe is defective..and always has been. At 106F I got a resistance of 3300 ohms. It should have been closer to 5600 ohms. So it’s reading the temperature as higher than it is. More like 130F according to the chart. So I will get a new probe. Now to solve the flow problem.
  • hot_rod
    hot_rod Member Posts: 18,210
    Sensors are not that expensive, worth a try. Get the part number from your manual
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • gloria
    gloria Member Posts: 11
    Just bought one.
  • HomerJSmith
    HomerJSmith Member Posts: 1,924
    edited December 2022
    My thoughts. Could the sys pump move more water than the boiler pump? I don't like the way the sys piping is connected to the boiler sys. The boiler piping is in a loop and the sys piping is taking supply thru the closely spaced tees. I would prefer that the sys piping being in a loop and the boiler piping supplying hot water thru the closely spaced tees. You would probably benefit by using a Hydro Separator.