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Problem with preheated water and Navien Tankless System

I have a Navien 240 A NG Tankless hot water heater. The unit dip switches are set for internal recirculating pump which I need to circulate the water to the back of my house. I have the unit set at 130 degrees. The unit works fine during milder weather.

To complicate matters, I have a geo thermal heat pump that generates hot water as a by product when it is operating. The hot water is pumped into a hot water storage tank. That storage tank is connected to the Navien. During colder days, it produces about 110-115 degree water that then feeds the Navien. This is where I run into problems. During colder days the Navien is receiving pre heated water at 110 - 115 degrees. For some reason, it will not fire and will not reach the 130 degree set point, when the source water is that high. The Navien works fine when the source water is less that 105ish.

I do not have the DIP switch # 6 set for storage tank use because if you have #6 on, it will not allow the recirculating pump to work. I need the recirculating for the back of my house.

Any suggestions?


  • GordyGordy Member Posts: 9,523
    edited January 2019
    Did you try raising the 130 to 140?

    Seems a waste of energy to raise 110-115 water to 130 when it’s plenty warm to use at that temp.

    If you are heating to 130 I hope you have a mixing device.
  • elheinenelheinen Member Posts: 1
    Thanks Gordy. I will try to raise the set point tonight. I lose about 10 degrees as it travels 75 - 80 feet to the back of my house. So 110 degrees is a little cool when it gets to the shower.
  • GordyGordy Member Posts: 9,523
    Do you have the manual? There is a commercial mode that allows you to go above 140. Not sure if yours has that feature.
  • HDEHDE Member Posts: 225
    edited January 2019
    Which model Navien do you have? You failed to give the full model number. The later models have a solar/geo dip swich setting to react differently to incoming heated water,
    In addition you mention you have the dip switch set for internal circulation yet you also say you have to have circulation to the back of the house. That requires settings for external circulation. Who installed this a professional trained installer?
  • eheineneheinen Member Posts: 2
    Yes, my model has the solar/geo dip switch. That is dip switch # 6 that I mentioned. However if you turn that switch on, it will not allow the recirculation to activate..

    You are correct, I have the dip switch’s set for external circulation, and circulation is working fine.

    Yes, a professional installed this system. He has exhausted his efforts to solve the problem. I’m pretty sure that he has not done an installation with a geo system.
  • mikeg2015mikeg2015 Member Posts: 1,178
    On a NPE240 without recirc I installed in a commercial kitchen as a booster heater, we had to install a mixing valve as about 90F was the max inlet water temp it would allow at any large volume.

    Not sure about other dip switches.

    Navien tech support is pretty good. You might cal them
  • hotnheatedhotnheated Member Posts: 1
    Not sure if you were able to fix your problem but I found this site with all the user manuals on it. If you can't find on there, I would just try and get ahold of them. However, they haven't been the most helpful on previous occasions ...
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