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Navien · Boiler

E046 Heat exchanger thermistor fault

Medium severity Navien NHB-HNavien NFB-H

What the control is telling you

The heat exchanger temperature sensor reading is abnormal. Manual action: check the thermistor connector.

Applies to: Navien NHB-H (NHB-055H/080H/110H/150H) and NFB-H fire-tube (NFB-175H/200H) condensing boilers

Likely causes

  • Loose, wet or corroded thermistor connector
  • Damaged wire
  • Failed thermistor

Test and repair steps

  1. Warning: Turn off power before removing the front cover.
  2. Reseat the heat exchanger thermistor connector and inspect the wire for damage.
  3. Compare the temperature readings in Status Info with actual water temperature.
  4. Replace the thermistor if the fault returns with a good connection.

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Source: Navien NHB-H Installation and Operation Manual, 11.14 Understanding Error Codes, p.119; Navien NFB-H Installation Manual, 11.7 Understanding Error Codes, p.116; NHB-H User's Information Manual (V1.0 Apr 2024), 5.2, p.24. Summarized in our own words; check the original manual for your model.

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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.