Navien Error Code E110: Exhaust Blockage — Meaning, Causes & Fix
Exhaust blockage / abnormal air pressure — Navien tankless water heaters (NPE, NPE-2; legacy display form 110). Navien's US user manuals name E110 'abnormal air pressure'; the NPE Service Manual and the NPE AWE/SWE table name the same code 'exhaust blockage (condensate blockage)'. The Service Manual's subcodes divide it: 1 = exhaust blockage (checking the fan), 2 = exhaust blockage (using hot water), 3 = exhaust blockage (using space heating). Manual reset.
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.
What causes the E110 code on a Navien water heater?
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.
A clogged intake air filter
Navien's maintenance section makes this branch official: a filter clogged by dust or lint stops the water heater with Error Code 110 displayed, and the prescribed cleaning interval is every 3–4 months. The filter sits inside the cabinet at the top left on the NPE-2, and a heater in a laundry room or a dusty utility space loads it far faster than the interval assumes. This is the E110 cause owners can both cause and cure — and the one that makes E110 the most preventable code on the platform.
A blocked condensate trap or drain
A condensing heater produces condensate continuously, and its drain path is part of the exhaust story: the Service Manual's APS diagnostics include checking the condensate trap and drain piping for obstruction or blockage, and the AWE/SWE table prints the code's name as 'exhaust blockage (condensate blockage)' — the parenthesis is Navien telling you the drain is a first-class suspect. A trap run dry, a drain line slimed shut or frozen, or a drain termination submerged will back water up until the air proof fails.
The fan cannot move the air it should
The fan provides combustion air and purges flue gas, and works with the APS to maintain gas input on long vent runs; its documented failure events include fan speed failure (RPM around zero), a loose fan assembly and disconnected or defective fan connections. E110 is listed among the fan motor's error codes, and the Service Manual's first E110 subcode is literally 'exhaust blockage (checking the FAN)' — the control distinguishes a path that is blocked from a fan that cannot push through a clear one, and so should you.
The air pressure sensor (APS) reports wrongly
The proof itself can fail: the APS detects the air pressure entering the burner system, and its documented failure event includes the case where it does not detect proper voltage. The Service Manual tests it electrically — wiring inspection, then its documented DC supply and signal ranges — after the pipes, filter and condensate have been proven clear. An APS that condemns a clear vent system is a sensor replacement, and it is diagnosed by elimination plus voltage, never by guessing.
Checks to run before you replace anything
- 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.
- Walk outside first, before any reset: look at both terminations (intake and exhaust) and the condensate drain outlet. Clear snow, ice, leaves or debris away from the openings from outside, and note anything you cannot clear — a nest inside the pipe, a crushed or separated joint, a termination installed where drifts bury it. Photographing the termination as found is genuinely useful evidence for a technician.
- Check the intake air filter — Navien's own maintenance item, on its 3–4 month cleaning interval: power off at the front panel, disconnect the power supply, remove the front cover, unfasten the filter assembly (top left of the unit on NPE-2), wash the filter with clean running water and a soft brush/toothbrush per the manual, dry it completely, and refit everything before reconnecting power. A filter that comes out grey and matted has already confessed.
- Check the condensate path you can see: is the drain line kinked, is its outlet frozen or submerged, is there standing water where the trap should drain? The trap and internal drain piping are technician territory, but a blocked external drain end is visible from outside and is part of the Service Manual's obstruction check.
- Note the subcode if your display shows one, and the circumstances: E110 at startup in a storm (termination/weather), E110 minutes into a long hot water run (condensate backing up, or a marginal path), E110 only on the coldest nights (freezing at the termination or drain). First-generation NPE units store the last 10 errors with subcodes in the error history (Info button, held over 2 seconds) — an E110 cluster on freezing nights reads differently from a daily E110.
- Reset once, by your generation's method (first-generation NPE: Reset button; NPE-2: Back button), only after the terminations and filter are dealt with, then run a long hot water draw and stay with the unit through it. An E110 that does not return through a full draw was the path. An E110 that returns on a proven-clear path has moved the diagnosis to the fan and the APS — technician tests, below.
Navien error code e110 how to fix
- Termination branch: clear the obstruction from outside and correct what invited it — a termination that drifts over needs its exposure addressed by an installer (relocation or an approved shield, per local code), and a pipe with a nest inside or a damaged/separated joint is vent-system repair, not a reset. Never cap, screen or narrow a termination with anything not approved for it: the 'fix' becomes next winter's blockage.
- Filter branch: clean the intake air filter exactly as the manual directs (wash, soft brush, dry completely, refit) and put it on the 3–4 month interval the manual prescribes — sooner in laundry or dusty locations. A filter too degraded to clean clean is replaced. This branch is the one complete owner fix for E110, and it should be exhausted before any part is suspected.
- Condensate branch: clear the drain obstruction — external blockage at the outlet by the owner; the trap, internal drain piping and any neutralizer media by a technician, who will also check why it blocked (a sagging drain line with a standing-water belly blocks again on schedule). A condensate blockage ignored becomes corrosion inside the unit as well as a repeating E110.
- Fan branch: a technician proves the fan electrically (its documented supply and signal ranges) and mechanically (assembly tight, connections seated), and replaces a fan that cannot reach or hold speed. Fan replacement is covers-off work on a combustion component — technician work, with a post-repair E110 watch through a full firing cycle.
- APS branch: with the path proven clear, a technician tests the APS wiring and its documented DC voltages and replaces a sensor whose output does not track reality. The discipline of this branch is its position: last. An APS replaced ahead of the termination, filter and condensate checks will faithfully report the same blockage the old one did.
The part that usually fails: Usually no part — an obstruction, the filter, or the condensate drain; the APS or fan only when a proven-clear path still fails
E110's parts discipline mirrors its cause order. The blockage family (terminations, filter, condensate) accounts for most E110s and costs no parts at all. The proof family costs one of two parts — the air pressure sensor, convicted by its voltage/output tests with the path clear, or the fan, convicted by its electrical and mechanical checks — and Navien's Service Manual structure (obstruction checks first, APS voltage checks after) is written to keep owners and technicians from buying the sensor for a snowdrift.
Navien e110 error code reset
E110 is a manual-reset code in the tankless tables: first-generation NPE resets with the front-panel Reset button (or by disconnecting and reconnecting power, per the Service Manual); NPE-2 resets with the Back button. The reset belongs after the path work, not before it: resetting an E110 whose termination is still buried or whose filter is still matted simply re-runs the air proof against the same obstruction and re-displays the code — or worse, clears briefly and fails mid-burn. One reset, after the outside checks and the filter, followed by a full hot water draw, is the test. An E110 that survives that test on a clear path is no longer a reset question at all; it is the fan/APS diagnosis, and repeated resetting only delays it.
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.
Why does the E110 code keep 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.
How to stop E110 coming back
- 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.
- A clogged intake air filter: Navien's maintenance section makes this branch official: a filter clogged by dust or lint stops the water heater with Error Code 110 displayed, and the prescribed cleaning interval is every 3–4 months. The filter sits inside the cabinet at the top left on the NPE-2, and a heater in a laundry room or a dusty utility space loads it far faster than the interval assumes. This is the E110 cause owners can both cause and cure — and the one that makes E110 the most preventable code on the platform.
- A blocked condensate trap or drain: A condensing heater produces condensate continuously, and its drain path is part of the exhaust story: the Service Manual's APS diagnostics include checking the condensate trap and drain piping for obstruction or blockage, and the AWE/SWE table prints the code's name as 'exhaust blockage (condensate blockage)' — the parenthesis is Navien telling you the drain is a first-class suspect. A trap run dry, a drain line slimed shut or frozen, or a drain termination submerged will back water up until the air proof fails.
Retrieving stored fault 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.
Other Navien water heater error codes
| Code | Meaning | First fix |
|---|---|---|
| E003 | Ignition failure — Navien tankless water heaters (NPE, NPE-2; legacy display form 003). The unit attempted ignition and no flame was detected. Navien's NPE Service Manual states the sequence exactly: in the case of an ignition failure, the water heater will attempt ignition 10 times; if no flame is detected, it displays E003, which is manually cleared. Manual reset. | Supply branch: restore the gas supply — open the valve fully, refill or replace the propane supply, or wait out/confirm the utility interruption with the gas supplier — then reset once and prove a full heating cycle. If static pressure reads normally but the unit fails under load, the fix is a technician's dynamic pressure test and correction of the supply sizing or connector, not a part inside the heater. |
| E004 | False flame detection — tankless (NPE/NPE-2): the control senses a flame signal when no flame should exist; auto reset in the NPE AWE/SWE table | Ensure the electrical cord is properly grounded (Navien's stated action). A standing E004 is technician work — a control that cannot trust its flame proof must not be run on resets |
| E012 | Flame loss — Navien tankless water heaters (NPE, NPE-2; legacy display form 012). The burner ignited and flame was proved, then the flame was lost during operation. Navien's user-manual actions for E012 are to clean the intake air filter and ensure the electrical cord is properly grounded. Manual reset. | Air branch: clean or replace the intake air filter and shorten its cleaning interval to the room's reality (the manual's baseline is every 3–4 months). Verify with a full-length hot water draw: an E012 cured by the filter stays cured under load, not just at startup. |
| E016 | Overheating of heat exchanger — tankless (NPE/NPE-2): the heat exchanger has overheated and the unit has shut down; manual reset. This — not E001 — is the tankless overheat code | Turn the system OFF for at least 30 minutes, then restart; clean the cold water inlet filter and flush the heat exchanger (Navien's stated actions). A repeating E016 needs a technician — never run an overheating exchanger on resets |
| E030 | Exhaust overheating — tankless (NPE/NPE-2): the exhaust limit shuts the unit down when flue temperature exceeds its limit (the US user manuals state 149 °F / 65 °C; the NPE Service Manual states 230 °F / 110 °C for over 10 seconds — a generational difference, same fault) | Turn OFF for at least 30 minutes, then restart; clean the cold water inlet filter and flush the heat exchanger (Navien's stated actions). Technician work if it returns |
| E031 | Overheating of burner — tankless, NPE-2 table: the burner itself has overheated. (Not listed in the first-generation NPE table checked; Navien's action for it in the NPE-2 manual is to contact technical support) | No owner fix is published: contact Navien Technical Support (1-800-519-8794) or a licensed technician. Do not reset and run a burner-overheat code repeatedly |
| E046 | Abnormal operation: limit control — tankless (NPE/NPE-2) (the NPE AWE/SWE table words the same code 'heat exchanger overheating sensor'): the heat exchanger's high-limit protection has operated or its sensor is abnormal; the Service Manual ties E046 to the high limit switch (with E016) | Navien's user manuals route E046 straight to Technical Support — licensed technician work. Treat it as an overheat code: let the unit cool and do not force operation |
| E047 | Abnormal operation: exhaust thermostat — tankless (NPE/NPE-2): the exhaust thermistor is open or shorted (Service Manual subcodes 1 = open, 2 = short) | Technician work: check the exhaust thermistor connection and the sensor, check the PCB connection (the Service Manual's stated checks). Navien's user manuals route E047 to Technical Support |
| E060 | Abnormal operation: dual venturi — tankless (NPE/NPE-2): the dual venturi limit switch operates abnormally (Service Manual subcodes cover its ON / close-OFF / open-ON states) | Technician work: check the dual venturi connection, test it in TEST mode, and check the gas orifice for obstructions. Navien's user manuals route E060 to Technical Support |
| E109 | Abnormal operation: fan motor — tankless (NPE/NPE-2): abnormal fan motor activity; manual reset. The fan provides combustion air and purges flue gas, working with the air pressure sensor | Clean the intake air filter (Navien's stated owner action). If E109 stands, a technician checks fan voltage and connections and cleans or replaces the fan motor |
| E127 | Abnormal operation: APS — tankless, FIRST-generation NPE (AWE/SWE) table only: the air pressure sensor is open, shorted, at an abnormal initial value or not answering; manual reset. The NPE-2 table does not carry E127 — on NPE-2 the same air-pressure proof is reported under E110 | Technician work: inspect and test the APS and its hose/connections and replace the sensor if it does not prove. Never bypass the APS — it is the venting proof the burner waits for |
| E407 | Hot water outlet thermistor open or short circuit — tankless (NPE/NPE-2) (AWE/SWE table: 'hot water outlet1 thermistor') | Technician work: check the thermistor and replace it if open or shorted (the Service Manual's stated action). Navien's user manuals route E407 to Technical Support |
| E421 | Cold water inlet 1 thermistor open or short circuit — tankless (NPE/NPE-2): the control cannot read incoming cold water temperature | Technician work: check the thermistor, verify its diagnostic value, replace the thermistor if open or shorted. Navien's user manuals route E421 to Technical Support |
| E432 | Cold water inlet 2 thermistor open or short circuit — tankless (NPE/NPE-2): the second cold water inlet temperature sensor reads open or shorted | Technician work: check the thermistor's voltage and resistance values and replace it if out of range (the Service Manual's stated checks) |
See the full list on the Navien Water Heater error codes hub.
Codes E110 gets confused with
E012 — Flame loss — Navien tankless water heaters (NPE, NPE-2; legacy display form 012). The burner ignited and flame was proved, then the flame was lost during operation. Navien's user-manual actions for E012 are to clean the intake air filter and ensure the electrical cord is properly grounded. Manual reset. E012 is a mid-burn failure, and its meaning is fixed by the moment it describes.
E003 — Ignition failure — Navien tankless water heaters (NPE, NPE-2; legacy display form 003). The unit attempted ignition and no flame was detected. Navien's NPE Service Manual states the sequence exactly: in the case of an ignition failure, the water heater will attempt ignition 10 times; if no flame is detected, it displays E003, which is manually cleared. Manual reset. 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.
Frequently asked questions
What does Navien error code E110 mean?
An air-path fault on Navien tankless water heaters (NPE/NPE-2). Navien's US user manuals call E110 'abnormal air pressure' — the air pressure sensor cannot prove the combustion air/exhaust path — while the NPE Service Manual and the AWE/SWE table call the same code 'exhaust blockage (condensate blockage)'. The manuals' stated actions are to ensure the exhaust pipe is free of obstructions and to clean the intake air filter; the Service Manual adds the condensate trap and drain piping to the obstruction check.
How do I fix Navien error code E110?
Work the air path in Navien's order: (1) check the outdoor intake and exhaust terminations and the condensate drain outlet for ice, snow, wildlife or debris and clear what you can from outside; (2) clean the intake air filter — Navien's maintenance section states a filter clogged with dust or lint stops the heater with Error 110, and prescribes cleaning every 3–4 months; (3) reset once and test with a long hot water draw. If E110 returns on a clear path with a clean filter, a technician tests the fan and the air pressure sensor — those are the code's remaining causes.
Is E110 the same as 'exhaust blockage' on a Navien?
Yes — they are two official names for one code. The US NPE and NPE-2 user manuals title E110 'abnormal air pressure'; the NPE Service Manual's error list titles it 'exhaust blockage' with subcodes for checking the fan and for hot water/space heating use, and the AWE/SWE user table adds '(condensate blockage)'. A page that treats them as different faults is splitting one code in two.
Can a dirty filter really cause E110?
Navien says so in as many words: its maintenance section states 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 on the front panel display. The filter starves the combustion air the APS is trying to prove. It is the first inside-the-cabinet check for E110 and the cheapest fix on this page: wash, dry completely, refit.
Why does my Navien show E110 only in winter?
That is the termination/condensate pattern: snow drifts burying a termination, ice forming at the exhaust lip or in the condensate drain outlet, and freezing condensate in an exposed drain run. The Service Manual's obstruction check names ice and snow first for a reason. Clear the termination and drain outlet, reset once, and if the pattern repeats every cold snap, the durable fix is at the installation — termination exposure and drain routing/freezing protection — which is installer work.
How do I reset Navien E110?
After the path checks, not before: first-generation NPE — press the front-panel Reset button (the Service Manual also documents disconnecting and reconnecting power); NPE-2 — press the Back button. Then run a full hot water draw. E110 is a manual-reset code, so it will wait for that press — but a press given to a still-blocked vent just re-runs the failed air proof. If the code returns with terminations clear and the filter clean, resetting is finished and fan/APS diagnosis begins.
What is navien error code e110?
Exhaust blockage / abnormal air pressure — Navien tankless water heaters (NPE, NPE-2; legacy display form 110). Navien's US user manuals name E110 'abnormal air pressure'; the NPE Service Manual and the NPE AWE/SWE table name the same code 'exhaust blockage (condensate blockage)'. The Service Manual's subcodes divide it: 1 = exhaust blockage (checking the fan), 2 = exhaust blockage (using hot water), 3 = exhaust blockage (using space heating). Manual reset. E110 is the code where Navien's two naming traditions meet, and reading both names together gives the truest picture of the fault.
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