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Navien · Tankless water heater

E016 Heat exchanger overheating

High severity Navien NPE-2

What the control is telling you

Water temperature in the heat exchanger went too high.

Applies to: Navien NPE-A2 (built-in recirculation) and NPE-S2 condensing tankless water heaters: NPE-150S2, NPE-180A2/S2, NPE-210A2/S2, NPE-240A2/S2

Likely causes

  • Clogged cold water inlet filter
  • Scale build-up in the heat exchanger (hard water)
  • Low water flow through the unit

Test and repair steps

  1. Clean the cold water inlet filter (and the recirculation inlet filter on A2 models).
  2. Flush the heat exchanger with a pump, hoses and descaling solution through the isolation valves for at least 45 minutes, then rinse 5 minutes.
  3. Check water hardness above 7 grains/gal a softener or Navien PeakFlow is recommended, above 12 grains/gal it is required.
  4. If an external recirculation pump is used, make sure it gives 2-4 GPM through the heater (not more than 4 GPM).
  5. Reset once with the Back button on the front panel and note whether the code returns.
  6. Code back after a reset? Stay at the unit and phone Navien Technical Support, 1-800-519-8794.

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Source: Navien NPE-A2/S2 User's Information Manual (20049624A), 5.2 Understanding Error Codes, p.17. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.