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Navien · Combi boiler

E439 No DHW flow detected / flow sensor fault

Medium severity Navien NCB-HNavien NFC-H

What the control is telling you

The DHW flow sensor is not reporting correctly (NFC-H: abnormal flow sensor). NFC-H manual lists the reset type as: Alarm.

Applies to: Navien fire-tube combi boilers, NFC-H series (NFC-250/200H, NFC-250/175H) and NCB-H combi boilers (NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H)

Likely causes

  • Clogged cold water inlet filter
  • Flow sensor wiring or failure
  • Hot water draw below 0.5 GPM

Test and repair steps

  1. Clean the DHW cold water inlet filter.
  2. Check Status Information > 15. DHW Flow while a tap is open (the boiler needs about 0.5 GPM to start DHW).
  3. Check the flow sensor connector and wiring.
  4. Code keeps returning? Phone Navien Technical Support, 1-800-519-8794.

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Source: Navien NCB-H Installation & Operation Manual, 11.7 Understanding Error Codes, p.129-130; Navien NFC-H Installation Manual, 11.7 Understanding Error Codes, p.127-128. 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.