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Navien · Tankless water heater

E407 Hot water outlet thermistor open or shorted

Medium severity Navien NPE-2

What the control is telling you

The control reads an open or short circuit on this temperature sensor.

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

  • Sensor unplugged or damaged
  • Wiring fault
  • Failed thermistor

Test and repair steps

  1. Turn off power and check the sensor connector and wiring for damage, corrosion or a loose plug.
  2. After restart, compare Status Information > 5. Out Water Temp with the actual water temperature.
  3. Reset once with the Back button on the front panel and note whether the code returns.
  4. Fix given 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.