Navien combi boiler error codes

40 codes with causes and test steps, plus 4 settings tables.

Code	Meaning	Severity
E001	Heat exchanger overheat	High
E003	Ignition failure	High
E004	False flame detected	High
E012	Flame loss	High
E016	Heat exchanger overheat (overheating of heat exchanger)	High
E030	Exhaust overheat (abnormal exhaust temperature)	High
E031	Burner overheat	High
E046	Heat exchanger thermistor / overheat sensor fault	Medium
E047	Exhaust thermistor fault	Medium
E060	Dual venturi fault	Medium
E109	Fan motor fault	High
E110	Exhaust blockage / abnormal air pressure (APS)	High
E205	Heating supply temperature sensor fault	Medium
E218	Heating return temperature sensor fault	Medium
E278	External (system) supply sensor not detected	Medium
E279	External (system) return sensor not detected	Medium
E302	Low water pressure (internal LWCO)	High
E351	Auto feeder (make-up water) valve fault	High
E352	High water pressure	High
E353	Water pressure sensor fault	Medium
E407	DHW outlet temperature sensor fault	Medium
E421	DHW cold water inlet sensor fault	Medium
E434	Water adjustment (flow control) valve fault	Medium
E439	No DHW flow detected / flow sensor fault	Medium
E441	DHW outlet 2 sensor fault	Medium
E445	Mixing (bypass) valve fault	Medium
E515	PCB fault	High
E517	DIP switch setting fault	Medium
E594	EEPROM fault	Medium
E615	Memory fault (input and memory)	Medium
E736	Cascade communication fault	Medium
E740	Outdoor sensor not detected	Low
E761	Pump aquastat (pre-heat aquastat) not detected	Low
E762	Vent pipe not fully inserted (VID)	Critical
E773	Improper gas type detected	Critical
E777	Low water cutoff (LWCO) activated	High
E782	Front panel communication fault	Medium
E784	Zone controller communication fault	Low
E786	Improper front panel	Medium
E788	Incorrect gas type setting	Critical

Settings and specs

Minimum installation clearances (indoor)

Clearances · Navien NCB-H

Side	Minimum
Top	9 in (229 mm)
Back	0.5 in (13 mm)
Front	4 in (100 mm)
Sides	3 in (76 mm)
Bottom	12 in (300 mm)

Indoor wall-hung only; ambient must stay above 32°F (0°C).
Do not install on carpet; leave room for service.

Source: Navien NCB-H Installation & Operation Manual, 2.1 Adequate Installation Clearances, p.15

Water quality limits (DHW and system fill)

Specifications · Navien NCB-H

Contaminant	Max allowed
Total hardness	200 mg/l (12 grains/gallon)
Aluminum	0.05 to 0.2 mg/l
Chloride	250 mg/l
Copper	1.0 mg/l
Iron	0.3 mg/l
Manganese	0.05 mg/l
pH	6.5 to 8.5
Sulfate	250 mg/l (DHW table); 205 mg/l (fill table)
Total dissolved solids	500 mg/l
Zinc	5 mg/l
Chlorine (fill water)	4 mg/l

Scale damage from poor water is not covered by warranty.
Manual shows sulfate 250 mg/l on p.23 and 205 mg/l on p.29 - check local guidance.

Source: Navien NCB-H Installation & Operation Manual, 3.2 About the DHW Quality p.23 and 3.5 Testing the Water System p.29

Minimum installation clearances (indoor)

Clearances · Navien NFC-H

Side	Minimum
Top	9 in (229 mm)
Back	0.5 in (13 mm)
Front	4 in (100 mm)
Sides	3 in (76 mm)
Bottom	12 in (300 mm)

Indoor wall-hung only; ambient must stay above 32°F (0°C).
Do not install on carpet; leave room for service.

Source: Navien NFC-H Installation Manual, 2.2 Adequate Installation Clearances, p.18

Water quality limits (DHW and system fill)

Specifications · Navien NFC-H

Contaminant	Max allowed
Total hardness	200 mg/l (12 grains/gallon)
Aluminum	0.05 to 0.2 mg/l
Chloride	250 mg/l
Copper	1.0 mg/l
Iron	0.3 mg/l
Manganese	0.05 mg/l
pH	6.5 to 8.5
Sulfate	250 mg/l (DHW table); 205 mg/l (fill table)
Total dissolved solids	500 mg/l
Zinc	5 mg/l
Chlorine (fill water)	4 mg/l

Manual shows sulfate 250 mg/l on p.26 and 205 mg/l on p.33.

Source: Navien NFC-H Installation Manual, 3.2 DHW water quality p.26 and 3.4 fill water p.33

Models covered

NCB-190/060HNCB-190/080HNCB-240/110HNCB-240/130HNCB-250/150HNFC-250/175HNFC-250/200H

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.