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Navien tankless water heater code E515: Circuit board fault

Tankless water heater, Canada and United States

The heater's main circuit board (PCB) is not operating normally.

This needs a licensed gas technician. There are a few safe checks you can do first, marked below. Anything inside the unit is a job for a professional.

What causes it

  1. The heater's power cord or the outlet it plugs into is not properly grounded.

    Check a Navien water heater's power cord is groundedYou can do this

    1. Find where the heater's power cord plugs in. If the heater has a plug, it should be a three-prong (grounded) plug that goes straight into a grounded outlet.
    2. Check the plug still has its ground prong, is not plugged in through a two-prong adapter or an extension cord, and that the cord is not damaged or modified.
    3. If you are not sure the outlet is grounded, or the heater is wired in with no plug, have a licensed electrician check the grounding.
      Do not open the heater or the outlet yourself.

    Clear a Navien error codeYou can do this

    1. Deal with the cause first, using the checks listed for the code.
    2. On NPE-A2 and NPE-S2 models, press the Back button on the front panel. On first-generation NPE-A and NPE-S models and on indoor NPN models, press the Reset button on the front panel.
    3. If an NR-21DU remote controller is fitted, you can press its OK button once instead. On outdoor NPN models, which have no front panel, the remote is the way to reset. The remote shows RST when the error is reset.
    4. If the code comes back, stop resetting. Note the code and the model number and contact Navien technical support or a licensed technician.
      Resetting over and over can hide a fault that needs a technician.

  2. The circuit board has a fault that needs a technician. Suspect this when the grounding is confirmed and the code comes back.

    Book a licensed gas technician

How to read this code on your unit

Booking a licensed gas technician

Contact Navien before booking a repairYou can do this

  1. Have the model number, serial number, purchase date, where the heater is installed and the error code ready.
  2. Call Navien Technical Support on 1-800-519-8794, or contact the company that installed the heater.
  3. For a repair under warranty, the installer or service provider must contact Navien before starting the work.

Book a licensed gas technicianlicensed gas technician

  1. Turn the unit off and leave the covers on. Gas components must only be serviced by a licensed technician.
  2. Note the code, how often it appears, and the model and serial numbers from the rating label.
  3. Book a licensed gas technician and give them those details.

Models that show this code

21 models in 6 ranges
RangeModels
NPE-A (first generation)NPE-180A, NPE-210A, NPE-240A
NPE-S (first generation)NPE-150S, NPE-180S, NPE-210S, NPE-240S
NPE-A2NPE-180A2, NPE-210A2, NPE-240A2
NPE-S2NPE-180S2, NPE-210S2, NPE-240S2, NPE-150S2
NPN-ENPN-120E, NPN-160E, NPN-180E, NPN-199E
NPN-UNPN-160U, NPN-180U, NPN-199U

Where this comes from

Checked against the manufacturer's manual on 9 October 2026.

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Other Navien tankless water heater codes

Code Meaning What you can do
E432 Cold water inlet temperature sensor 2 fault Call a pro
E434 Water adjustment valve fault Call a pro
E438 Circulation pump fault Safe checks first, then a pro
E439 Flow sensor fault Call a pro
E441 Hot water inlet temperature sensor 2 fault Call a pro
E445 Bypass mixing valve fault Call a pro
E517 DIP switch setting error Call a pro
E593 Front panel button fault Call a pro
E594 Memory chip (EEPROM) fault Call a pro
E615 Input and memory fault Call a pro
E736 Cascade communication fault Call a pro
E740 Outdoor temperature sensor fault Call a pro

See all control board fault codes on tankless water heaters across brands.