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Navien · Tankless water heater

E740 Outdoor temperature sensor abnormal (with air handler)

Low severity Navien NPE-2

What the control is telling you

Outdoor reset is on but the outdoor sensor is missing or reads out of range.

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

  • Outdoor sensor not connected
  • Sensor or wiring fault

Test and repair steps

  1. Check the outdoor sensor wiring at the H2Air controller.
  2. If outdoor reset is not wanted, set H2Air DIP switch 1 ON (outdoor reset off). While the error is active the system runs as if outdoor reset were off.
  3. Check Status Information > 16. AHU Outdoor Temp.
  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.18. Summarized in our own words; check the original manual for your model.

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