Navien Water Heater Error Codes List: Every Code Explained

Every Navien water heater error code we could verify against Navien's own documentation — what it means, what usually causes it, and the first fix to try — in one table. Codes differ between model series, so treat your model's tech sheet as the final word.

How to read and retrieve error codes on Navien water heaters

A Navien tankless unit reports on its front panel display, and the panel is generation-specific. First-generation NPE units show the error in the manuals' E-form (E003) and navigate with dedicated buttons the Service Manual names: Information (Info), Diagnostics, +/-, Reset and Power. NPE-2 units use the EZNav panel — Menu, Back, OK, Up and Down — around a display that shows combustion/error status, recirculation and cascade status, a status/flow readout with the current flow rate, and the temperature setting alongside the code. Two details matter. Many codes carry a subcode that narrows the fault (E110's subcodes separate fan-check, hot-water and space-heating blockages; E615's name which input is out of range), and the subcode is part of the diagnosis. And the unit remembers: the Service Manual documents an error history on first-generation NPE (Info held over 2 seconds; the 10 most recent errors, labelled 0–9, with elapsed hours and subcodes), and the NPE-2 installation documentation carries an equivalent Viewing Error History function. Photograph the display, subcode included, before resetting.

The complete Navien water heater error code list

How to reset / clear error codes on Navien water heaters

Navien documents two reset forms, one per panel generation, and they are not interchangeable. First-generation NPE: press the Reset button on the front panel — the Service Manual adds the alternative of disconnecting, then reconnecting electrical power to the water heater. NPE-2: press the Back button — the NPE-2 User's Information Manual gives that as the reset in both its operating section (3.3) and its troubleshooting section, and notes the unit retains its settings through a power outage. A reset clears the display and lets the unit retry; it does not clear the underlying condition, and the manuals' tables divide codes into manual-reset codes (which wait for your press: E003, E012, E016, E110 among them), auto-reset codes (which clear when the condition passes: E004, E046, E782 among them) and alarms (E760's flushing/service alarm). If resetting does not solve the problem, both user manuals give the same next step: the troubleshooting table, or Technical Support at 1-800-519-8794.

How to diagnose any Navien water heater code

Work the problem in this order — and stop wherever gas piping, the burner compartment, venting or the temperature-and-pressure relief valve begins, because those belong to a licensed technician: (1) record the report exactly — a counted LED flash pattern, a numeric display code, or a smart-control alarm are three different languages, and a photograph or video beats a memory of any of them; (2) establish the water story: is there no hot water at all, water that runs cold mid-draw, or water but with a code — tankless codes split into ignition, flame, airflow/venting, flow and temperature families, and tank codes into ignition, sensor and control families, and the family picks the checks; (3) run the owner-level external checks for that family first: power and the unit's switch, the gas cock fully open, intake and exhaust terminations clear of snow, nests and debris, the inlet water filter or screen rinsed (tankless), the condensate trap and drain not blocked or frozen (condensing models), and on tank models the status light read before anything is reset; (4) reset once, the way the brand documents, and run hot water at one tap while you watch — a code that returns at the same stage (fan start, ignition click, flame light, sustained burn) is an active fault naming its stage, not a glitch; (5) everything past that line — flame sensors and igniters inside the burner, gas valves, heat exchangers, control boards — is professional work with the gas supply and a meter involved. Two standing cautions: never plug or cap a dripping T&P relief valve (it is reporting pressure or temperature, and it is the tank's last safety device), and treat any gas smell as an emergency — leave and call the gas utility. Scalding is the quiet hazard in every reset: a control fault that lets outlet temperature drift high is a reason to stop using the water on skin until the code is resolved.

The 002 and 302 caution: boiler codes wearing tankless numbers

Two numbers on this hub are named without meanings, deliberately, and this note is their explanation. Navien sells two different machines under one brand: tankless water heaters (NPE, NPE-2, NPN), which heat domestic water on demand and have no heating circuit, and boilers (the NCB combi-boilers and the NHB/NFB lines), which heat a sealed central-heating circuit filled with water at pressure. The boilers monitor that circuit, and their manuals define E302 around it: in the NCB300 combi-boiler manual, the NFB-H boiler manual and Navien's system-boiler manual alike, E302 is 'low water pressure' — the heating circuit's pressure has fallen and the boiler stops until it is restored. E002 belongs to the same boiler low-water family in Navien's older boiler documentation. Neither code appears in any tankless table checked for this hub — NPE-2, first-generation NPE, AWE/SWE or the NPE Service Manual — for the physical reason that a tankless unit has no sealed heating circuit and no circuit pressure to lose. The trap: an owner searches 'Navien 302', lands on boiler pages (most Navien 302 content online is boiler content), and goes looking for a pressure gauge and filling loop their water heater does not have. If a tankless display seems to show 302, record it exactly — code, subcode, model, serial — and put it to Navien Technical Support rather than to a boiler procedure: codes get misread (E030 is the tankless exhaust-overheat code), and displays show subcode forms. On a row where a borrowed meaning can send an owner to the wrong machine's repair, no meaning is the honest entry.

One platform, several dialects: E-forms, bare numbers, subcodes and two names for E110

Navien's tankless documentation speaks in dialects, and most contradictions between Navien pages dissolve once the dialect is named. The same fault appears as E003 in current manuals and as bare 003 in older documents and in the display's own history mode, where the first digit is the history position and the remaining three are the code. Many codes carry a subcode — a second number that narrows the fault within the code (E110's subcodes separate a fan-check blockage from hot-water and space-heating blockages; E407/E421 split open from short; E615's name which sensor input or memory segment is out of range) — so two owners with 'the same code' can have different faults, and a service call that omits the subcode throws away the most specific part of the report. Names drift too: E110 is 'abnormal air pressure' in the US user manuals and 'exhaust blockage (condensate blockage)' in the Service Manual and AWE/SWE table — one code, two official titles. Even numbers move: the US user manuals give E030's flue-temperature shutdown at 149 °F (65 °C) while the Service Manual gives 230 °F (110 °C) sustained over 10 seconds — different generations, both Navien, and this hub prints the disagreement rather than averaging it. Working rules: quote the code exactly as displayed, subcode included; name your model and generation (NPE versus NPE-2) in every search; and treat any source that decodes a Navien number without naming its platform and generation as a draft, not an answer.

Manual reset, auto reset and alarm: the third column is part of the code

Navien's error tables carry a column most online code lists throw away: how the code clears. It is diagnostic information, and the tankless tables use three values. Manual reset codes — E003, E012, E016, E030, E109, E110, E127, E434, E445, E515, E517, E615 among them — hold the unit shut down until a person resets it (Reset button on first-generation NPE, Back button on NPE-2, or a power disconnect/reconnect). Navien reserves this for codes where a human should look before the burner tries again: ignition, flame loss, overheating, air-pressure proof. Auto reset codes — E004, E046, E407, E421, E432, E441, E736, E740, E782 among them — clear themselves when the reported condition passes; they are mostly sensor and communication reports, and one that keeps reappearing is logging a condition that keeps recurring, which the error history shows even when the panel looks clean between events. Alarm entries do neither: E760, the flushing/service alarm, is the type specimen — a maintenance demand, not a failure. Reading the column changes behaviour in both directions. A manual-reset code that 'keeps coming back after I reset it' is not defying the reset; it is re-detecting its condition on the retry. An auto-reset code that has vanished by the time you reach the unit has not healed; it has passed, for now, and its history entry — with the hours since the previous error, on the first-generation panel — is the evidence to work from. Quote the code, the subcode and the reset behaviour when you call: Navien's technical support works from the same three columns.

The most searched Navien water heater codes, in detail

E003 — Ignition failure

E003 is the Navien tankless platform's failed-light report, and its definition contains the whole diagnosis: the burner was commanded to light, the ignition sequence ran — repeatedly, up to ten attempts on the Service Manual's account — and the flame rod never reported a flame. That makes E003 a report about a chain, not a part. For a flame to be proved, gas must arrive at the right pressure, the gas valve must open, the igniter must spark at the correct electrode gap, the burner must light, and the flame rod must sense the flame and report it through a sound ground path to the PCB. E003 says the chain produced no proved flame; it does not say which link failed, and Navien's own check list for the code walks the entire chain in order: gas supply valve and supply pressure first, then the electrode gap and flame rod condition, the ignition transformer's operation, the gas control valve's operation, the flame rod's wiring and grounding, the air pressure hose and sensor, the PCB DIP switch settings, the gas orifice plate's match to the gas type, collected water in the flue or air supply on vertical vent installations, and the ground connection screws on the heat exchanger — with PCB replacement named only if the issue continues despite all of those checks. Two practical consequences follow. First, the commonest E003 is an supply event, not a dead part: a gas valve left closed after other work, a utility interruption, an empty propane tank or a pressure problem will produce a textbook E003 on a perfectly healthy heater, which is why Navien's user-level action for the code is a single, humble check — ensure that the main gas supply valve is open — and why an E003 that appears once after gas work and never again is usually exactly that story. Second, an E003 that returns after the supply is proven is a component story told in the Service Manual's order: spark, valve, sensing. Note what separates E003 from its neighbours, because the three codes are constantly confused: E003 means flame was never proved at light-off; E012 means flame was proved and then lost mid-operation; E004 means flame is being reported when there should be none. An owner who reports the exact code saves the technician the first half hour, because each of the three starts at a different link of the same chain.

Most likely cause: No gas, or gas at the wrong pressure (the supply branch) — Navien's check list opens here for both E003 and E012: is the main gas supply valve open, and is the supply pressure within the operating range? The Service Manual's gas-supply check method adds the field detail: measure static pressure (standing) and dynamic pressure (at maximum combustion), because another gas appliance firing can pull dynamic pressure down even when static pressure reads fine; an undersized or overtightened flexible connector can do the same. A closed valve after plumbing work, a utility outage and an empty LP tank are this branch's everyday members.

First check: SAFETY: E003 is a gas code. If you smell gas, leave, do not touch electrical switches or use a phone in the building, and call the gas supplier or fire department from outside — that is the manual's own instruction, and it outranks every check below. Never open the burner compartment or test gas components as an owner.

If it keeps coming back: An E003 that returns has a signature worth reading. Return immediately, every attempt, with no sound of sparking: the igniter/transformer branch. Sparking heard, a brief light or whoomph, then failure: the sensing branch (flame rod, wiring, ground) or a valve that opens and drops. Return only under heavy hot water demand or when other gas appliances run: dynamic gas pressure — the supply is adequate standing still and inadequate working. Return after weeks of normal running, worsening gradually: electrode fouling or a weakening component. Quote the pattern and the interval; on E003, when it fails is most of what the technician needs.

E012 — Flame loss

E012 is a mid-burn failure, and its meaning is fixed by the moment it describes. The ignition sequence succeeded — gas flowed, the igniter sparked, the burner lit and the flame rod proved the flame — the unit settled into heating, and then, with hot water still being demanded, the flame went away or its proof did. Everything about E012 follows from that sequence. Because light-off succeeded, the causes that produce a pure E003 (a valve that never opens, an igniter that never sparks) are largely acquitted; because the loss happens under way, the suspects are the things that can fail a running flame: a gas supply that sags under load, combustion air that falters, a flame that lifts or destabilises, and a flame-sensing circuit that loses a flame that is actually still there. Navien's own documentation maps exactly those territories. Its service check list for E012 asks whether the main gas line valve is open, directs checking the gas pressure against its operating range and the gas meter's BTU capacity, sends you to the flame rod and its diagnostic value, and then lists the intake air filter, the ground wire and the power supply — finishing with tightening the ground connection screws on the heat exchanger. That list quietly contains the code's central subtlety: an E012 can be a lost flame or a lost report of a flame, and the two feel identical from the tap — hot water runs, then goes cold, and the display shows E012. The manual's remedies for the user are the two that touch both stories without opening the gas train: clean the intake air filter (a starved air supply genuinely destabilises a running flame) and ensure the electrical cord is properly grounded (flame sensing is an electrical measurement that leans on the ground path; a poor ground loses real flames on paper). The component sections fill in the service side: the main gas valve's documented error codes are E003 and E012 — a valve that opens for ignition and then cannot hold or modulate is an E012 suspect — and the burner section names dust or soot deposits on the burner surface and unstable flame conditions among its failure events, with flame loss among its effects. An E012, read properly, is therefore not 'the flame sensor code' or 'the gas code': it is the running-flame code, and its diagnosis is the short list of things that can take a proved flame away — supply, air, burner condition, valve behaviour, and the sensing path that reports it all.

Most likely cause: Gas pressure that sags under load — The Service Manual's E012 list is supply-first: main gas line valve open, gas pressure within the operating range, and the gas meter checked for proper BTU capacity. A running burner draws far more gas than an ignition attempt, so a supply that is adequate at light-off can starve a flame at full fire — an undersized meter or line, a regulator problem, a propane supply running low, or other appliances pulling the same supply down. An E012 that arrives at peak demand, or when the furnace and stove run together, is this branch confessing.

First check: SAFETY: flame loss is a combustion event. If you smell gas at any point, the manual's instruction governs: do not try to light anything, do not touch electrical switches, leave and call the gas supplier or fire department from outside. Soot, scorching or a CO alarm moves any E012 straight to a technician, with the unit off.

If it keeps coming back: Read a returning E012 by its interval and its company. Shortening intervals over weeks: a flame rod or ground path deteriorating, or a burner fouling progressively. Returns only at peak household demand: dynamic gas pressure, full stop — the heater is the messenger for a house supply that cannot feed everything at once. Returns after electrical work in the home: the ground branch until a technician proves otherwise. Returns with combustion noise or a changed burner sound: burner condition. And an E012 that begins appearing alongside E110s is telling one story in two codes — the air path (filter first) is failing both the proof and the flame.

E110 — Exhaust blockage / abnormal air pressure

E110 is the code where Navien's two naming traditions meet, and reading both names together gives the truest picture of the fault. 'Abnormal air pressure' names the measurement: the air pressure sensor (APS) watches the pressure of the air entering the burner system, the fan provides combustion air and purges flue gas, and the control will not fire — or will not keep firing — a burner whose air side it cannot prove. 'Exhaust blockage' names the usual reason the measurement goes wrong: something in the intake, exhaust or condensate path is obstructing the flow the APS is trying to verify. The Service Manual's APS section spells out why the control is unforgiving here: a failed air-pressure proof produces combustion noise, imperfect or abnormal flame, and — its words — excessive carbon monoxide emissions, with the water heater not operating. That is why E110 is a shutdown code rather than a warning: a condensing tankless heater that cannot move its air and exhaust freely is a heater that can burn dirty, and Navien stops it instead. The blockage family is wider than owners expect. It includes the outdoor terminations (the Service Manual lists ice, snow and wildlife as obstruction examples, checked across the intake, exhaust and condensate drain pipes), the intake air filter inside the cabinet — Navien's maintenance section is blunt that if the air intake filter becomes clogged by dust or lint, the water heater will cease to operate and Error Code 110 will appear, and directs cleaning it every 3–4 months — and the condensate path, because on a condensing unit a blocked condensate trap or drain piping backs water up into the exhaust route; the APS diagnostic list includes checking the condensate trap and drain piping for obstruction or blockage by name. Beyond blockage sit the proof components themselves: the fan (E110 is one of the fan motor's two documented error codes, with E109) and the APS, whose wiring and output voltages the Service Manual tests when the pipes prove clear. Read E110, then, as an air-path verdict with an order of suspicion: terminations, filter, condensate, then the fan and sensor that prove the path. Most E110s are weather, lint and water. The ones that are not are the sensor lying about a clear path — and telling those apart is the entire diagnosis.

Most likely cause: A blocked outdoor termination — ice, snow, wildlife, debris — The Service Manual's first E110 check, across all three pipes: check the intake, exhaust and condensate drain pipes for obstructions — its examples are ice, snow and wildlife. A termination capped by a snowdrift, an intake screened over by a nest or leaves, or an exhaust outlet frozen at its lip all strangle the air path at its easiest-to-check point, which is why an E110 that arrives with the weather is this branch until proven otherwise. Construction debris belongs here too: a termination left taped, capped or buried by landscaping or siding work after installation blocks the path as completely as any storm.

First check: SAFETY: E110 is a venting code on a gas appliance, and venting is carbon monoxide territory. Never run the heater with a vent termination you know is blocked, never disconnect vent piping to 'test', and treat any CO alarm, soot at the termination or a combustion smell as a stop-and-call event. The outdoor checks below are visual only — do not reach into or dismantle vent piping.

If it keeps coming back: A returning E110 keeps a diary, and its entries are legible. Returns with storms, snow or hard freezes: the termination or the condensate outlet is exposed to the weather that causes it — an installation exposure problem, fixed at the termination, not in the cabinet. Returns weeks after a filter cleaning, in a dusty season: the filter interval is too long for the room the heater lives in. Returns gradually, with longer runs needed to trigger it: a condensate path narrowing, or a fan weakening toward the speed it can no longer hold. Returns immediately at every startup on a clear path: the APS proof itself. Each pattern names its branch; a technician told 'E110, third time, always during the longest showers, drain outlet was frozen twice' starts halfway down the list.

Less common and model-specific codes

Search data shows owners also meet these codes on Navien water heaters: NPE-240A, Navien. They are not part of the core code list Navien publishes for most models — several are series-specific, abbreviated display readings, or codes carried over from a sister platform — so we do not publish meanings for them rather than guess. Treat them by symptom: note what the machine was doing when the code appeared (filling, draining, heating, spinning), run one full power cycle (5 minutes off), and if the code returns, match the symptom to the closest documented family in the table above and check the tech sheet stored inside your machine for the model-specific definition.

Deep-dive guides for the most searched codes

Related guides

Facts on this page were checked against manufacturer documentation: hvacmarket.ca · navien.co.uk · manualspro.net · cdn3.guidespdf.com · manualspro.net · manualmachine.com · manualmachine.com