Navien Tankless Water Heater Error Codes

Updated October 13, 2026 · by Aurora Star Tech Inc.

33 Navien Tankless Water Heater error codes and diagnostic codes, with causes and troubleshooting steps for each. Select a code, or find your model below.

Homeowner with a tankless water heater problem? Call (647) 657-2977 or book a service call — licensed technicians across Vaughan and the GTA.

Navien Tankless Water Heater error codes list

Code	Meaning	Severity
E003	Ignition failure	High
E004	False flame detection	Medium
E012	Flame loss	High
E016	Heat exchanger overheating	High
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
E21	No hot water	Medium
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

Find codes by Navien model

Navien NPE-2

NPE-150S2 NPE-180A2 NPE-180S2 NPE-210A2 NPE-210S2 NPE-240A2 NPE-240S2

Navien NPN

NPN-120E NPN-160E NPN-160U NPN-180E NPN-180U NPN-199E NPN-199U

Tankless Water Heater troubleshooting guides

No hot water All brands · Tankless Water Heater
Water temperature fluctuates All brands · Tankless Water Heater
Hot water slow to reach fixtures - Navien NPE-2 Navien · Tankless Water Heater
Hot water turns cold - Navien NPE-2 Navien · Tankless Water Heater
No water from hot tap - Navien NPE-2 Navien · Tankless Water Heater
Water not hot enough or too hot - Navien NPE-2 Navien · Tankless Water Heater

Navien Tankless Water Heater specs and setup data

Installation clearances (indoor / outdoor) Navien · Tankless Water Heater · Navien NPE-2
Installation clearances (indoor / outdoor) Navien · Tankless Water Heater · Navien NPN
Water quality limits and flushing schedule Navien · Tankless Water Heater · Navien NPE-2

Homeowner help: Tankless Water Heater No Hot Water: What to Check

General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.