What do Navien error codes mean? NPE-2 tankless code table

Before you use this table

If you smell gas, do not reset anything. Leave on foot, avoid anything that can spark, and call the gas utility and 911 from a safe place^[3].

This table covers the Navien NPE-2 condensing tankless line (NPE-180A2, 210A2 and 240A2, and the matching S2 models). The meanings are our paraphrase of the NPE-2 user's manual, not Navien's text^[1]. For other Navien models, use the manual on Navien's downloads page^[2].

"Power cycle once" means turning the unit off and back on one time. If the code returns, stop.

Navien NPE-2 code table

Code	What it means	Safe homeowner check	Call a pro when
E003	Ignition failure: the burner did not light	Main gas valve to the unit open; other gas appliances work; propane not empty	Still no light: gas pressure, igniter or flame rod
E004	False flame: flame sensed when there should be none	Unit plugged into a properly grounded outlet	It returns: flame rod or board diagnosis
E012	Flame lost after lighting	Clean the intake air filter per the manual; check the grounded outlet	It returns: gas supply or vent diagnosis
E016	Heat exchanger overheating	Clean the cold water inlet filter; schedule a flush	It returns after both: descaling or sensor checks
E030	Exhaust too hot; the unit shuts down above about 149 F flue temperature	Clean the inlet filter; schedule a flush	It returns: exhaust sensor and vent checks
E031	Burner overheating	None	Always
E046	High-limit safety tripped or abnormal	None	Always
E047	Exhaust temperature sensor open or shorted	None	Always: sensor replacement
E060	Dual venturi fault	None	Always
E109	Fan motor fault	Clean the intake air filter	It returns: fan replacement
E110	Abnormal air pressure: blocked exhaust or intake	Clear snow, nests or debris from the outside terminals; clean the intake filter	It returns: vent repair
E407	Hot water outlet temperature sensor open or shorted	None	Always: sensor replacement
E421, E432, E441	Other water temperature sensors open or shorted (cold inlet 1, cold inlet 2, hot water inlet 2)	None	Always
E434	Water flow adjustment valve fault	None	Always
E438	Circulation pump fault (pump or air handler setups)	Note whether the pump hums or vibrates, and tell the pro	Always
E439	Flow sensor fault	None	Always
E445	Bypass mixing valve fault	None	Always
E515	Main circuit board fault	Confirm a grounded outlet; power cycle once	It returns: board replacement
E517	DIP switch setting error	None	Always: installer settings need correcting
E593, E594, E615	Front panel key, memory or input faults	Power cycle once	It returns
E736	Cascade (multi-unit) communication fault	None	Always
E740	Outdoor temperature sensor fault (air handler setups)	None	Always
E760	Flushing or service reminder	Book a flush or routine service	n/a
E762	Vent pipe not seated properly at the unit	Turn the unit off; do not run it	Always: a loose vent can leak exhaust
E773, E788	Gas type mismatch: the unit or its settings do not match the gas supplied	None	Always: gas settings are licensed gas work
E782	Main panel communication fault	None	Always
E785	Flow switch or sensor fault (air handler setups)	None	Always

Source: Navien NPE-2 User's Information Manual^[1], paraphrased.

Myth: E515 is the outlet sensor

You will find websites that list E515 as the hot water outlet sensor. Navien's NPE-2 manual says otherwise: E407 is the outlet sensor, and E515 is the main circuit board^[1]. A sensor and a board are very different parts and prices, so check the manual for your exact model before anyone orders parts.

The two filters that clear many Navien codes

Navien units have two owner-serviceable filters, and dirty ones show up behind several codes^[1]:

• Cold water inlet filter. A clogged one restricts flow and can cause overheating codes (E016, E030).
• Intake air filter. A dirty one can cause flame loss and fan faults (E012, E109, E110).

The owner's manual shows how to reach and clean both. If either code returns after cleaning, call a pro.

Hard water and E760

E760 is a reminder, not a failure. Scale builds inside the heat exchanger over time, especially in hard water, and leads to overheating codes if it is ignored. HomeGuide's 2025 range for a tankless flush and descale is $75 to $300^[4].

When to call a pro

• E762 (vent not seated) or E773 and E788 (gas type mismatch): turn the unit off.
• Any overheat code that returns after cleaning the inlet filter.
• Any sensor, valve, pump, fan or board code.
• E003 or E012 that returns with gas confirmed on.