Navien boiler error codes

33 codes with causes and test steps, plus 2 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 (check flow / system filters)	High
E030	Exhaust overheat	High
E031	Burner overheat	High
E046	Heat exchanger thermistor fault	Medium
E047	Exhaust thermistor fault	Medium
E060	Dual venturi fault	Medium
E109	Fan motor fault	High
E110	Exhaust blockage	High
E205	Heating supply temperature sensor	Medium
E218	Heating return temperature sensor	Medium
E278	External system supply sensor not detected	Medium
E279	External system return sensor not detected	Medium
E291	Return temperature higher than supply	Medium
E302	Low water pressure	High
E352	High water pressure	High
E353	Water pressure sensor fault	Medium
E480	DHW tank sensor not detected	Low
E515	PCB fault	Medium
E517	DIP switch setting fault	Medium
E594	EEPROM fault	Medium
E615	Memory fault	Medium
E736	Cascade communication fault	Medium
E740	Outdoor sensor not detected	Medium
E762	Vent pipe not fully inserted (VID)	Critical
E777	Low water cutoff activated	High
E782	Front panel communication fault	Medium
E784	Zone controller communication fault	Medium
E786	Improper front panel detected	Medium
E788	Incorrect gas type setting	High

Settings and specs

Installation clearances (indoor)

Clearances · Navien NHB-H

Side	Minimum clearance
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)
Vent to combustibles	0 in

Bracket gives 5/8 in (16 mm) from the wall; studs at 16 in on centre.
Common vent installs: 36 in above the top and 24 in in front are recommended for service.
Do not install on carpet; indoors only.

Source: Navien NHB-H Installation and Operation Manual, 2.1 Adequate Installation Clearances p.13-14; 1.3 p.7; 9.1 p.79

Installation clearances (indoor)

Clearances · Navien NFB-H

Side	Minimum clearance
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)
Vent to combustibles	0 in

Do not install on carpet; indoors only.
Remove the wood pallet and refit the 6 screws to keep the cabinet airtight.

Source: Navien NFB-H Installation Manual, 2.2 Adequate Installation Clearances p.15; 1.3 p.8; 2.1 p.13-14

Models covered

NFB-175HNFB-200HNHB-055HNHB-080HNHB-110HNHB-150H

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.