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Navien · Boiler

E030 Exhaust overheat

High severity Navien NHB-HNavien NFB-H

What the control is telling you

Flue gas temperature exceeded the limit. Manual action: check flow and clean system filters.

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

Likely causes

  • Low water flow through the heat exchanger
  • Dirty system filters
  • Return water too hot for the PVC exhaust limit
  • Exhaust thermistor fault

Test and repair steps

  1. Check flow through the boiler and clean the system return filter (see flow checks under E001).
  2. Read Exhaust Temp in Status Info while firing.
  3. Note with DIP SW2 #8 OFF the control limits exhaust to about 149°F (65°C) for PVC venting. Only set #8 ON if the exhaust is CPVC, approved PP or stainless steel.
  4. Check the return temperature setting/heat load; return water above 140°F (60°C) needs high-temperature vent material and SW2 #8 ON.
  5. If the reading looks wrong, check the exhaust thermistor connector (see E047).

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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.