Navien 240a external recirculation settings with thermal comfort valve.

Discussion in 'Tankless Water Heater Forum' started by dradam, Sep 24, 2017.

  1. dradam

    dradam New Member

    Joined:
    Sep 21, 2008
    Location:
    Washington, DC
    Tech support is not open yet:

    Just had installed a Navien 240a. Using the internal pump to set up an external re circulation line through the cold water system as return with a Grundfos comfort valve at the last fixture in the line. This seems relatively new for Navien and is in a recent Navien technical bulletin from 04/18/16.

    The system is working as worked through by Navien tech support.

    1) Two way valve set to external
    2) Dip switch 1: on 2: off (making it look like internal recirculation)
    3) Parameter 17 set to on- "Enable thermal bypass valve". (I am told by tech support that this lets the unit recirculate with much lower flows)

    So here's my question:

    The above system is working and sending warm water to may last fixture on schedule-- but it doesn't stay warm and I get a bit of a lukewarm sandwich until the full system kicks in.

    How do I keep the water at the last fixture as hot as possible during scheduled recirculation times?

    There is mention of :

    Parameter 12 : Pump cycle interval time (20 is currently default)
    Parameter 14: Return line sampling time (30 is currently default)

    I am not sure how or if I should adjust these.

    When the recirc schedule turns on it seems that my unit will then shut off when the cold water return to the unit is about 86 degrees. The water in the hot line then cools down (creating a sandwich) before recirc turns on again.

    So what is the endpoint shutting off the recirc?:

    Is it a temp parameter back at the unit?
    Is it a flow sensor at the unit shutting off when the Grundfos valve closes at 99 degrees slowing return flow ?

    Will changing parameters 12 or 14 resume recirc sooner ?

    If anyone has a pdf of technical bulletian 2016-A-001 and 002 I would love to read them.

    Thanks for your Input.
     
  2. CPTJOE

    CPTJOE New Member

    Joined:
    Mar 1, 2018
    Location:
    South Carolina
    I don't have any answers to your questions, but I am curious to know how you like the overall setup?

    I just had a Navien 240-A installed a week ago with the same type of recirculation using the cold water line and a Grundfos comfort valve at the furthest fixture. Honestly, I'm not totally sold on the setup and thinking about switching to the internal recirculation mode to see how it compares.

    The Grundfos is loud, especially just before it closes, which seems to cycle about every 20 minutes. It's installed under a sink in the master bathroom, and the bed is about 5 feet away on the other side of the wall. I have some mass load vinyl in the wall (sheet rock has't been replaced yet) to try and deaden the sound but it's still about as loud as a toilet filling. Thinking about moving the Grundfos to the washing machine line or even the utility sink in the garage. Both are about as far as the master bath from the water heater but I'm not sure how it will affect things. The other thing I don't like is the cold water is warm where the Grundfos is.

    The Navien itself is about as far away from the fixtures as possible. It's mounted outside close to the gas main in and replaced a tank water heater in the attic. With the external recirculation we don't have to wait for hot water very long, and haven't experienced any sandwiches, but I don't like using the cold line for recirculation.
     
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  4. dradam

    dradam New Member

    Joined:
    Sep 21, 2008
    Location:
    Washington, DC
    Thanks for your inquiry. I have had the system for a number of months now and overall I really like it. My home is long and used to have two water heaters, one on either side of the house. Now with a single NPE240A and the re circulation I can keep hot water to the last fixture in the home. Replacing one NPE for two 90 gallon tanks ( one dead and one likely to die) was a cost savings even though the NPE and recirc is expensive.

    Regarding your concerns. My grunfos is not near the bedrooms. So I don't hear it. I have the Navilink and app which allows me to set schedules for re circulation and heating-- so it really only is set to work during waking hours. Perhaps moving the valve to another location might help you even if it is not at the end fixture .

    There are parameter settings on the unit that when set can tell it how long to recirculate for, and the timing and interval to check the water temp.

    I am still trying to tweak these and have not gotten clear info from Navien. If I take a shower and it is just when the recirc is running it is great-- hot water almost immediatly, but if it has reached temp and not circulated for a bit I still sometimes get a bit if a cold water sandwich because the water in the lines has had a chance to cool down before the system does a temp test and recirc . I have been afraid to lengthen the circulation and testing times because if the grundfos valve truly closed at 99 degrees I don't want the recirc pump to burn out. I am not really clear if the valve closes at 99 degrees or is still just one way.

    Warm water in the cold line has not been a concern for me. I only recirc in the mornings and tend to shower first in the am so the warm water is just sucked back with the cold.

    Even If I had a dedicated re circulation line I think I would still have to get the recirc settings tweaked to avoid a cold water sandwich, but with out the grundfos this might be easier. I am contemplating adding a true re circulation line, but it would not be easy.

    I have one frustration with the navien app. You can buy a hot button upgrade that can connect to your phone and turn recirculation on or off, or you can set a schedule through the navilink, but not both. I would like to keep my am schedule, but if would be nice if it had a software solution "hot button" so I could recirc before and afternoon shower as needed. I hope someone from Navien reads this and responds.

    Despite some of the growing pains, when running I think the recirc savees me on water and the system must be saving me on gas. I love the endless hot water. I also got about 400$ in rebates with it so overall very happy. It simply has to continue to work flawlessly forever now.....

    Best of luck, post again if I can be of help.
     
  5. HimuraMOdo

    HimuraMOdo New Member

    Joined:
    Aug 17, 2018
    Location:
    Colorado
    Hey Dradam,

    I'm going to do the same to my heater and when I did the google research and found your post.

    Not sure if that's the root cause to your issue. But based on this manual, it's recommended to have a 120V normal close solenoid valve installed to avoid colder than desired DHW temperature. Here is the note from the manual:

    "The solenoid valve controls and limits the flow of cold water in the recirculation system. If a solenoid valve is not installed, DHW temperature may be colder than the set temperature."

    Here is the link to it:
    https://mans.io/files/viewer/460869/26

    https://mans.io/files/viewer/460869/28

    Also, a check valve is needed at the cold water inlet. But you probably have it installed already.

     
    Last edited: Aug 17, 2018
  6. Matthew Tanner

    Matthew Tanner New Member

    Joined:
    Tuesday
    Location:
    pearson ga
    Did you ever get any answers on parameters 12 and 14? Also did the parameter 17 Enable thermal bypass valve help and how did you turn it on. We are using the navilink system to set recirc timers but I am not certain it is functioning well.
     
  7. dradam

    dradam New Member

    Joined:
    Sep 21, 2008
    Location:
    Washington, DC
    Hi Matthew,

    Just saw your post. Unfortunately 2 years later I am still baffeled by my recirculation settings. I find that my unit continues to recirculate off of schedule. At first I was told it was a problem with the app. More recently I was told It has somthing to do with the Navien servers that did not communicate with the zip code in my app. I have changed the zip code twice now, but I still find the unit recirculating on its own off of the schedule. I really can't comment on the best parameters for 12 an 14 and I dont think most of the tech support staff understands either. If your research uncovers anything I am all ears. Sorry I cant help more at this point.
     
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