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Navien NB-150 DHW Priority

Afternoon. Just would like to know if anyone else experienced this item. New Navien NB-150 boiler installed. The default setting for the outdoor reset I changed from finned tube baseboard to Low mass setting. Essentially it was changed to wood flooring with the temperature range for supply from 80-140 F and the return set point range at 70-116 F. This is good for the house and the floors. What I noticed was that the indirect DHW storage tanks' aqustat was calling for hot water five times an hour. What was happening is that the cooler wood floor water was being pumped through the indirect tank and cooling the water down to the point that the aquastat called for more hot water to be pumped through. There is a parameter setting on the boiler that has the default "ON" that the DHW circ pump will be on when there is a call for heat. That parameter was changed to off. The DHW circulator pump still runs when there is a call for heat. I called Navien countless times with their response it is the wiring. I traced all of the wiring and it was done correctly. One of the third level fellas said it was time for the multimeter. I gave them all of the readings. When there is a call for DHW only the DHW circulator pump runs and the supply pump and the return (boiler) pump shuts off. That is how the parameters were set at the factory. When there is call for DHW the two main pumps have continuity but they do not run as factory set. The call for heat all three pumps run. The intresting part is on the zone control and the aqua stat. When there is a call for heat the zone control on the boiler is showing continuity and the aquastat is showing 26AC. With that piece of information Navien decided to ship a new board and the installer swapped out the old one for the new one. The end result is no difference. I decided to do a custom outdoor reset with a minimum temperature of 120. I am matching the hot water so the indirect does not cool down. The lowest I can go for the max range was 157 degrees. So the outdoor reset has a range of 120 to 157 degrees. At this time the calls for hot water has stopped. I am keeping an eye on the floors to ensure they are in the 80 degree range and not getting too hot. At this time its ok. I dont think this is ideal and boiler is not working as designed. Wanted to know if anyone else had this and what they had to do to get around this and also does anyone have any other ideas? Also what was done with the custom outdoor reset would there be issues with that? Appreciate the help.


  • DZoroDZoro Posts: 1,015Member
    Picture time :) Please post some pictures of the entire system at a couple angles.
  • newinnjnewinnj Posts: 31Member
  • newinnjnewinnj Posts: 31Member
  • newinnjnewinnj Posts: 31Member
    Howdy, if you need any closeups or other pics please drop a line. I will try to get some out there.
    Appreciate the help!
  • DZoroDZoro Posts: 1,015Member
    What size pumps are on the injection loop off the boiler, and main heat pump, and domestic? Do the pumps have any check valves installed inside them?
  • newinnjnewinnj Posts: 31Member
    Hi the pumps are the following
    The injection loop: TACO 0100-F3-1 IFC
    Main heat pump: TACO 0100-F3-1 IFC
    DHW pump: TACO 007-F5
    Answer to your question they are IFC circ pumps and I don't know if the installer kept the check valves in or not from my understanding from reading other posts that they can be removed.

    Other stuff
    Zone Valve Controller TACO ZVC406 6 zone
    Honeywell Aquastat
    The manifolds are from a company that went out of business called Radiant Direct
    Mr.PEX Actuators
  • clammyclammy Posts: 2,415Member
    You need flow checks in the pump and also a flow check on the return line also .this happens because of thermal migration the reason being your tank temp is higher then your radiant set point . Install a pump w a ifc hopefully on the supply and then put on flow by the tanks return . It s the only way I set up indirects zero migration issues ever .peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • newinnjnewinnj Posts: 31Member
    I am thinking the IFC are still in the supply and return. Would a flow check help on the DWH pump? Even with flow checks installed when the heat is called all pumps runs (supply, return and DHW) and that is the source of the problem. If the wood floors have a lower temperature then the indirect then over time the indirect is going to get cooled down. I do agree more flow checks is a good thing but I don't know if that will overcome this specific issue.
  • newinnjnewinnj Posts: 31Member
    Clammy, Thanks for your advice.

    On the call with the boiler support several times. Also finally had some time to play with the DHW pump to run tests. The call for heat happens the DHW pump is totally disconnected and a supply of cooler water is going to the floors. In fifteen minutes without the pump connected the call for DHW happens. The indirect tank got cooled down quickly with the cooler floor water flowing through it. The end result I I will be installing check valve or an IFC pump on the supply and also a check valve on the return side. Appreciate the help! I will post again once this is all done and results are in. Two questions. to the board. First one does it mean that when the heat call is happening that the indirect tank's heating coil water was runnning in reverse? So any water in the coil was going reverse and getting replaced with cooler floor water? Second question is this a common mistake not having check valves or the installer should have known better. In one of the indirect water tank schemas there is a note from the boiler company to have IFC or check valves installed. 2 pumps were IFC and the DHW was not. Thanks again for the help.
  • DZoroDZoro Posts: 1,015Member
    It's not a common mistake to not install check valves, or at least it shouldn't be. It's common knowledge for a installer to understand simple pumping flows.
    It is also common pump piping to install pump isolation flanges so that pump work can be done without re- purging the system.

    Have them install the check valves there should not be any additional charges to you.
  • newinnjnewinnj Posts: 31Member
    I realized I never closed the final results. Navien diagrams and the Navien support mentions all pumps need to be IFC. That is what Clammy called out for. I called the installer and he replaced the DHW pump with an IFC pump. It is working nice now. I will keep Clammy advice for another check valve for the domestic return for future project. Thanks all!
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