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Navien · Combi boiler

E016 Heat exchanger overheat (overheating of heat exchanger)

High severity Navien NCB-HNavien NFC-H

What the control is telling you

The heat exchanger overheated, typically from poor water flow or scale inside the heat exchanger. NFC-H manual lists the reset type as: Manual reset.

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

  • Scale/sludge in the heat exchanger
  • Low system flow or air in the system
  • Clogged heating strainer

Test and repair steps

  1. Turn the boiler off for at least 30 minutes, then restart it (the manual's listed remedy).
  2. Check system pressure, purge air and confirm the boiler pump runs.
  3. Clean the space-heating return filter.
  4. Flush the heat exchanger power off, close the heating supply/return isolation valves (C and D), connect a circulation pump and hoses to the flush valves (A and B), circulate the cleaning solution per the solution maker's time, then rinse with fresh water for 5 minutes.
  5. Refill, purge air and test.
  6. 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.