Navien NPE 240A Parameter list.

Discussion in 'Tankless Water Heater Forum' started by dradam, Nov 23, 2019.

  1. dradam

    dradam Member

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    I finally have my Navien NPE 240 A scheduling working, but I want to tweak the parameter settings to try and get the hottest water to my farthest fixture and keep it hot during the scheduled recirculation times. I want to tweak the Parameters a bit to minimize a cold water sandwich. Does anyone here have a list of the parameter settings for this unit? Thanks
     
  2. Dana

    Dana In the trades

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    There are no parameter settings that have any effect on the cold water sandwich issue. The flue purge and ignition delays are baked in the cake, and not adjustable, so the cold water sandwich will remain. Insulating both the supply and return plumbing on the recirculation loop to R3 (per current code) or better can sometimes reduce, but not fully eliminate the cold water sandwich.

    Have you taken the time to read the manuals thoroughly?
     
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  4. zl700

    zl700 DIY Senior Member

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    Here it is (P12-P15)
     

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  5. dradam

    dradam Member

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    In response to zl700 thank you for the parameter list.In response to Dana, Thank you for responding. I have read the manuals thoroughly . Its a shame they do not include a detailed list of the parameters there. I am not clear as to why the cold water sandwich can not be improved. I am using the Navilink and App to set recirculation schedules. Recirculation through my cold water system- no dedicated line.

    I will share some of my thinking . please correct me if I am wrong.

    P12-- was set to 5 minutes by my installer based on time that it took the pipes to get warm at my farthest fixture. I increased this to six minutes and saw more consistent temperatures at my farthest fixtures.

    Theory: At 5 minutes the fixture was getting warm, but with the additional minute more hot water was recirculating back toward the Navien. Essentially warming more of my cold water lines. My shower has a balanced valve so that when open new heated water would now mix with more return line warm water ( In the cold system) stretching out the time frame until the navient burner kicked in again with my demand.... less sandwich.

    P14: Theory: I believe The water in my recirculation system cools down pretty quickly. Because my system was installed in existing construction I do not have a dedicated return line and I can not access the existing lines to insulate them.

    This parameter appears to tell the unit how often to sample the return line to check for a temperature drop. Default is 30 minutes, but I belive there is is a lot of temperature drop off in that 30 minutes. I have just set this parameter to 15 minutes with the thinking that it will reheat more frequently if it the NPE senses that temp drop.

    P15: The text in this parameter is slightly unclear to me-- but as I think as I understand it the the burner will turn off during a recirulation when it sees a specified differential between set temp and return temp. Default differential is 9 degrees. If I set the default to the lowest differential, 5 degrees wouldn't the burner stay on longer ? This is further unclear to me because I belive the Navicirc (and /or Grundfos) valves shut between 85- 90 degrees. If that is the case will the Navien ever see return line samples above this temp? If not then the differential will always be greater than the default or lower. So is this parameter even relevant?


    So, Dana, I understand what you are saying about the flue purge and ignition delays being fixed, and I can't add more insulation to my lines, But does the thinking above make any sense in terms of keeping the hottest and most consistent water in my lines at least during a scheduled recirculation?

    Thanks.
     
    Last edited: Dec 5, 2019
  6. Dana

    Dana In the trades

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    I am not clear as to why the cold water sandwich can not be improved.

    There is a minimum amount of time between when the water flow is detected and the burner firing, since the flue has to be purged of potentially explosive gases before activating the ignition. That minimum time will never go away, and during that time water is flowing through the heat exchanger without being heated, thus there will always be a cold/tepid water sandwich. This is the very definition of the "cold water sandwich" problem inherent with all tankless heaters. Insulating the pipes or changing the delta-T differential parameter does not particularly help that problem. It's not a matter of the burner staying on longer, it's a matter of how much delay there is before ignition.

    If you are seeing some other/bigger/longer cold or tepid water issues related to how the recirculation system is controlled it's something elses, and normally referred to as "cold water sandwich".
     
  7. dradam

    dradam Member

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    Thank you for your reply I am still hugely happy with my system.
     
  8. Dana

    Dana In the trades

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    I'm happy you're happy.

    My 'mercan syntax was a bit garbled on the previous post.

    Part of what I had meant to say was that issues with the recirculation control don't fall under the "cold water sandwich" definition, even though the symptoms might have some similar characteristics. (But re-reading it it doesn't parse that way- my English will get better someday- it has to, since I can't afford an editor. :) )
     
  9. dradam

    dradam Member

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    No worries Dana and thank you again. I understand what you are saying and it makes perfect sense. That said I feel that my changing the parameters has helped. While it can not prevent the delay in cold water being heated when called for ( as you have explained) I feel like I am softening the blow by effectively keeping a hotter temperature in my pipes during a scheduled recirculation cycle. Almost like a buffer to the temperature drop. With no dedicated recirculation line I get warm water in the cold system too at least for a while. My balanced (antiscald) shower valve must blend this warmer water too. I also believe that the warm pipes themselves must raise the temp of the cold water infusion that happens before the boiler kicks in. There is likely a temperature drop at some point but I have not really has a "cold" sandwich in a while.

    Many thanks again.
     
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    FWIW, a pressure balanced valve will change the outlet temperature if either the hot or cold water supply changes..it's only proportioning the balance between the two supplies. If you want to have a chance of keeping the shower outlet temperature fairly consistent, change the valve to a thermostatically controlled one. If you happen to have a Delta R10000 rough-in valve, it's just change the cartridge and trim package.
     
  11. dradam

    dradam Member

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    Thank you that makes sense as well. My system is grohe with a temp regulator and then a separate flow control.
     
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