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Navien · Boiler

E218 Heating return temperature sensor

Medium severity Navien NHB-HNavien NFB-H

What the control is telling you

Return water sensor fault. 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 or damaged return thermistor connector
  • Failed sensor

Test and repair steps

  1. Warning: Power off. Reseat the return thermistor connector and inspect wiring.
  2. Compare Return Temp in Status Info with actual pipe temperature.
  3. Replace the sensor if the reading is wrong.

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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.