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Bleeding a Navien boiler zone..

AmatGonzi Member Posts: 10
edited November 2023 in Domestic Hot Water

I have an existing Navien boiler (NH-150) that has an indirect Peerless water heater. The current system has 4 zones, but when constructed, had the stubs for a fifth zone. I'm currently remodeling an area that will require this additional zone. My question, is about bleeding air out of this new zone once it's in place. In my older 80% efficient boiler, before this new one was installed, it was usually a matter of isolating the zone you wanted to bleed, and turn on the fast fill, and open the drain for that zone, to bleed the air. But this heating system (as you will note in the picture attached) is way more complicated). I have tried to make the attached picture very clear, noting where all the components are. Red and blue arrows indicated the general flow of the water when the heater is on and one or more zones are calling for heat. The water line is noted in green. The white on red numbers indicate where there is a drain/shutoff valve, or a spigot. I've noted in white on blue lettering some of the major components of the system such as circulators. Zones are controlled by a Taco zone controller.

I would like to know 1) How to bleed any individual zone (new or existing). 2) In addition I don't think you would need to also bleed the boiler if you are just interested in bleeding a downstream zone, but I'm asking just in case.



  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,060
    This system could have been designed a little better, but since it is working as build I would not change anything. Install the new radiators in the same configuration as the existing radiators.
    In order to get air from any of the heat zones you will need to open the zone valve for that zone. Close the isolation valve you have labeled #1. Close the isolation valve you have labeled #4 open the fast fill on the autofeed and watch the pressure get above 25 PSI. Allow the expansion tank to store the extra water from the increase in pressure to help in the force purge to move the air out of the zone/loop. When the gauge reaches 25 PSI open the hose bib # 2 and let the pressure force the air out backwards. As I said this is not ideal but this is how your installer set it up.

    I would have set it up to purge in the same direction of flow as the system operates, but that’s just me.

    The yellow dotted line shows the flow of the purge water. See how it goes in the opposite direction of the operating flow? This will not work if there are Flo-check valves in the system. You will need to manually open them if that is possible. Circulators with IFC built in will make this procedure impossible. If that does not work, let me know and I will look for another way. The original installer was able to do it so I think this will work.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • AmatGonzi
    AmatGonzi Member Posts: 10
    edited November 2023
    I understand there are some taco circs that have FC's built in but the model numbers on those end with "IFC". I have the following: Boiler/System Circulator (007-F5). Do I need to be concerned with closing off all the other zones and/or the intake to the DHW water tank as well, or leave them alone?
  • AmatGonzi
    AmatGonzi Member Posts: 10
    Sorry one more question, you said #4 in my diagram but that's just a hose spigot, I assume you are referring to the shutoff at the base of the manifold labeled #5?