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Navien · Combi boiler

E278 External (system) supply sensor not detected

Medium severity Navien NCB-HNavien NFC-H

What the control is telling you

The system supply sensor is not detected. Occurs when the heating control method is set to system supply temperature. 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

  • System sensor not installed or disconnected
  • Wiring fault
  • Control method set to Sys Supply without a sensor

Test and repair steps

  1. Check Status Information > 8. Sys Supply Temp.
  2. Check the system sensor wiring at the PCB.
  3. Without a system sensor, go to Space Htg Operation > 5. SH Control Method and pick Supply or Return Temperature.
  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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