Navien tankless water heater error codes

33 codes with causes and test steps, plus 3 settings tables.

Code	Meaning	Severity
E003	Ignition failure	High
E004	False flame detection	Medium
E012	Flame loss	High
E016	Heat exchanger overheating	High
E21	No hot water	Medium
E030	Exhaust overheating	High
E031	Burner overheating	Critical
E046	Limit control abnormal	High
E047	Exhaust thermistor open or shorted	Medium
E060	Dual venturi abnormal	High
E109	Fan motor abnormal	High
E110	Abnormal air pressure	High
E407	Hot water outlet thermistor open or shorted	Medium
E421	Cold water inlet 1 thermistor open or shorted	Medium
E432	Cold water inlet 2 thermistor open or shorted	Medium
E434	Water adjustment valve abnormal	Medium
E438	Circulation pump abnormal (with air handler)	Medium
E439	Flow sensor abnormal	Medium
E441	Hot water inlet 2 thermistor open or shorted	Medium
E445	Bypass mixing valve abnormal	Medium
E515	PCB abnormal	High
E517	DIP switch setting abnormal	Medium
E593	Front panel key abnormal	Low
E594	EEPROM abnormal	High
E615	Input and memory abnormal	High
E736	Cascade communication abnormal	Medium
E740	Outdoor temperature sensor abnormal (with air handler)	Low
E760	Flushing / service alarm	Low
E762	Vent pipe not properly inserted	High
E773	Wrong gas type detected	Critical
E782	Main / panel communication abnormal	Medium
E785	Flow switch / sensor abnormal (with air handler)	Medium
E788	Gas type mismatch: DIP switch vs panel setting	Medium

Settings and specs

Installation clearances (indoor / outdoor)

Clearances · Navien NPE-2

Side	Indoor	Outdoor
Top	9 in. (229 mm)	36 in. (900 mm)
Back	0.5 in. (13 mm)	0.5 in. (13 mm)
Front	4 in. (100 mm)	24 in. (600 mm)
Sides	3 in. (76 mm)	3 in. (76 mm)
Bottom	12 in. (300 mm)	12 in. (300 mm)

Vent clearance to combustibles is 0 in.
Outdoor: use the Navien Outdoor Vent Kit; keep 3 ft from an eave to the top of the vent terminals; mild climates only.
Keep room temp between 32 F (0 C) and 125 F (52 C).
Common vent installs: 36 in. top and 24 in. front recommended for service.

Source: Navien NPE-A2/S2 Installation Manual, 3.1 Adequate Installation Clearances, p.17; Outdoor Installation, p.59

Water quality limits and flushing schedule

Water quality · Navien NPE-2

Hardness	grains/gal (mg/L)	Treatment	Flush frequency
Soft	0-4 (0-60)	None	None
Moderately hard	4-7 (61-120)	None required	Once a year
Hard	7-9 (121-160)	Softener or Navien PeakFlow recommended	Once a year
Very hard	9-12 (161-200)	Softener or PeakFlow highly recommended	Residential once a year; commercial twice a year
Extremely hard	>12 (200)	Softener or PeakFlow required	-

Other max levels: hardness 200 mg/L, chloride 250, copper 1.0, iron 0.3, manganese 0.05, sulfate 250, TDS 500, zinc 5, chlorine 4 mg/L; aluminum 0.05-0.2 mg/L; pH 6.5-8.5.
Flushing is advised when no treatment device is installed; use white vinegar or a tankless descaler.
Damage from poor water quality is not covered by warranty.
Manual's flush column for moderately hard to hard rows is merged - read as once a year.

Source: Navien NPE-A2/S2 Installation Manual, 3.1 About Water Quality, p.15

Installation clearances (indoor / outdoor)

Clearances · Navien NPN

Side	Indoor: combustibles	Indoor: non-combustibles	Outdoor: combustibles	Outdoor: non-combustibles
Top	6 in. (152 mm)	2 in. (51 mm)	12 in. (305 mm)	2 in. (51 mm)
Back	0 in.	0 in.	0 in.	0 in.
Front	6 in. (152 mm)	6 in. (152 mm)	Panel 24 in. (610 mm); exhaust 24 in. (610 mm)	Panel 0 in.; exhaust 24 in. (610 mm)
Sides	2 in. (51 mm)	1/2 in. (13 mm)	6 in. (152 mm)	1/8 in. (3.2 mm)
Ground / bottom	12 in. (305 mm)	12 in. (305 mm)	12 in. (305 mm)	2 in. (51 mm)
Vent	0 in.	0 in.	-	-

Room temp must stay between 32 F (0 C) and 120 F (49 C).
Outdoor models need a weather-rated disconnect switch for the 120 V supply.
Indoor models: rated to 10,100 ft (3,078 m). Outdoor models: under 4,500 ft only.

Source: Navien NPN-U/NPN-E Installation Manual, 3.1 Adequate installation clearances, p.17; 3.6, p.47; 3.7.2, p.49

Models covered

NPE-150S2NPE-180A2NPE-180S2NPE-210A2NPE-210S2NPE-240A2NPE-240S2NPN-120ENPN-160ENPN-160UNPN-180ENPN-180UNPN-199ENPN-199U

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.