What error codes does a Navien water heater or boiler display?

Navien condensing tankless units (NPE-A2, NPE-S2) and combi-boilers (NCB-E) plus the NHB hydronic boilers all use E-prefix three-digit fault codes on the front-panel display. Codes group roughly into combustion / ignition (E003 ignition failure, E012 flame loss, E016 heat-exchanger overheat, E030 exhaust overheat), high-limit and venturi safety (E046 high-limit, E060 dual venturi), air pressure / venting (E110 air-pressure differential), thermistor / sensor (E407 hot outlet, E421 cold inlet 1, E432 cold inlet 2, E441 hot inlet 2), water-flow and pump (E434 adjustment valve, E438 circulation pump on combi models, E439 flow sensor), controller and front panel (E515 PCB communication, E593 front-panel key), and cascade / service (E736 cascade communication, E760 service alarm). Press the front-panel Reset button after correcting a soft fault; persistent codes need diagnosis using the IOM for your specific model and serial-number range.

What does E046 mean on a Navien tankless water heater?

E046 indicates the high-temperature limit control switch has detected an out-of-range condition. The switch opens when water temperature inside the heat exchanger exceeds approximately 197.6°F (92°C), cutting power to the burner circuit as a safety lockout. Common causes: broken or detached wires at the high-limit switch connector, switch resistance below 1.0 Ohm (failed switch must be replaced with the OEM part number for your model), a genuine overheating condition driven by scale buildup or restricted water flow, or a PCB failure misreading the limit-switch signal. Diagnose by powering down, inspecting the wiring harness for burnt insulation or loose push-on connectors, and measuring switch resistance with a multimeter — a reading below 1.0 Ohm confirms switch failure. If the switch tests good, investigate scale and inlet-filter restriction as the underlying overheating cause. Navien Technical Support is reachable at 1-800-519-8794 for parts verification.

What does E060 mean on a Navien condensing unit?

E060 flags an abnormal condition in the dual venturi limit switch — the component on Navien condensing models that controls the air/gas mixing ratio at each firing stage. The PCB monitors the dual-venturi position feedback; when the switch signal is missing or out of expected range during a firing sequence, the unit shuts down and locks out. Common causes: loose or damaged wiring harness connector at the dual venturi, mechanical binding of the actuator, a failed dual-venturi limit switch that no longer sends position feedback, a PCB communication fault, or an obstructed gas orifice. Diagnose via the dual-venturi test routine in the service menu — watch for actuator travel through full range. Replace the dual venturi if test mode confirms the actuator does not move or does not stop at the correct position. After any venturi work, a licensed technician must verify combustion with an analyzer and confirm CO levels at the exhaust before returning the unit to service.

What does E110 mean on a Navien tankless water heater and how do I fix it?

E110 means the air-pressure differential switch detected combustion-air pressure outside acceptable limits. The unit monitors both intake and exhaust pressure; when a blockage, clogged filter, or condensate-trap problem disrupts the pressure balance, the PCB shuts down the burner and logs E110. Top causes: exhaust vent blocked at the exterior termination by debris, ice (especially in winter), bird nests, or leaves; intake air filter clogged with dust, lint, or insulation fibers; condensate trap blocked, preventing drainage and creating back-pressure; damaged or disconnected vent pipe; failed air-pressure differential switch. Fix sequence: inspect both intake and exhaust terminations for obstructions and ice dams, remove and clean the intake air filter (Navien recommends every 3–4 months under normal conditions), flush the condensate trap with clean water, walk the entire vent run pressing each push-fit or twist-lock joint to confirm full seating, and only after that test the air-pressure switch with a manometer per the service manual's pressure spec.

What does E432 mean on a Navien water heater?

E432 indicates the cold water inlet 2 thermistor has faulted open or short. On multi-heat-exchanger Navien models (dual-HX NPN configurations), a second cold-water inlet thermistor monitors the second heat exchanger's cold-side inlet temperature independently of the first; when its signal falls outside the valid resistance window, the PCB logs E432 and shuts the unit down to prevent uncontrolled water heating. Common causes: thermistor probe failed open or short internally, wiring harness connector corroded or disconnected at the second-inlet location, wire insulation damaged near the heat exchanger causing a short to chassis, or PCB thermistor input-channel failure. Diagnose by disconnecting the harness, inspecting both connector sides for corrosion and bent pins, measuring resistance against the IOM resistance-temperature chart at current ambient, and checking the live diagnostic value in the service menu — a reading stuck at maximum, minimum, or 0 confirms sensor failure.

What does E438 mean on a Navien combi-boiler and is it the same on tankless models?

E438 indicates abnormal circulation-pump operation — specifically on Navien 'A' combi-boiler models (NCB-E and similar) where an internal circulation pump moves heated water through the space-heating loop. When the PCB detects the pump is not running, running at the wrong speed, or drawing abnormal current, it logs E438 and stops the heating cycle (domestic hot water often still functions). Pure tankless water heaters (NPE-A2, NPE-S2) do not produce E438 because they have no internal space-heating circulator. Common combi causes: seized pump motor or impeller mechanically blocked, supply or return valves closed, flow-sensor malfunction reading zero flow even with pump running, air lock preventing pump pressurisation, or PCB pump-output circuit failure. Diagnose by verifying water-line valves are open, purging air through the pump bleed screw, manually rotating the pump shaft via the bleed port, inspecting the flow sensor for debris, and running the pump test routine in the service menu before replacing the pump.

What does E515 mean on a Navien condensing unit?

E515 indicates an internal PCB communication fault — the main control board lost data exchange with the ignitor board, fan motor driver, dual-venturi actuator, or 3-way valve. The fault display includes a subcode that identifies which path failed: subcodes 1–8 point to the ignitor board, subcode 9 points to the fan motor (this is the well-documented “515-09” variant), and subcodes 10–12 point to the dual-venturi feedback loop. Common causes by subcode: loose or damaged connector between the PCB and the identified peripheral, fan motor or wiring fault on subcode 9, dual-venturi actuator failure on subcodes 10–12, missing chassis ground (which causes electrical noise that corrupts communication and is a frequent root cause across all subcodes), or PCB internal failure. First verify the unit is properly grounded — chassis-ground continuity to the electrical-panel ground bar — then inspect the connector at the subcode-identified peripheral before suspecting the PCB itself.

How do I troubleshoot Navien E003 ignition failure or E012 flame loss?

E003 means the burner attempted ignition but the flame rod never confirmed flame; E012 means the burner lit but lost flame mid-cycle. They share most root causes. Sequence: confirm the main gas valve is fully open and other gas appliances in the building are operating normally (rules out utility-side issues); inspect and clean the flame rod by removing the burner cover and gently polishing the probe with fine emery cloth (carbon deposits weaken the ionization signal); check the igniter electrode for cracked ceramic and correct spark gap per the service manual; clear the intake air filter at the bottom of the unit (the dominant E012 cause is a clogged filter starving combustion air); walk the full intake and exhaust vent run for blockages, ice dams, or disconnected joints; and verify the chassis ground wire is securely fastened at both the unit frame and the electrical panel ground (a poor ground prevents the PCB from reading flame ionization). If E003 / E012 returns after all of those, the gas valve, flame rod itself, or PCB needs technician-level diagnosis.

What does E760 mean on a Navien tankless water heater?

E760 is a flushing / service-alarm reminder, not a failure code — it appears when the unit's internal service-interval timer reaches the configured maintenance threshold (typically the annual service mark). The unit continues to produce hot water normally while E760 is active, so it does not interrupt operation; ignoring it is what causes problems, because the heat exchanger continues to scale and eventually trips genuine fault codes like E016 (heat-exchanger overheat) or E030 (exhaust overheat). Resolution requires technician-level service: descale the heat exchanger by circulating a Navien-approved (or food-grade equivalent) descaling solution through the service ports for the manufacturer-recommended duration, clean the cold-water inlet filter, flush crystallized scale out of the condensate trap, then — critically — reset the service timer in the service menu. Failure to reset the timer leaves E760 active even after correct maintenance. In hard-water regions, set a calendar reminder for annual professional service to head off E016 / E030 lockouts.

When should I call a service technician for a Navien fault?

Several Navien E-codes always require a licensed technician: E046 with a confirmed-good limit switch (the PCB or heat-exchanger assessment is needed), E060 dual-venturi replacement (post-install combustion verification with a CO₂ analyzer is mandatory), E515 with a subcode that persists after grounding and connector checks (the PCB itself is failing), E434 water-adjustment-valve replacement (requires service-menu valve recalibration), E438 circulation-pump replacement on combi models (requires draining part of the heating loop, refilling, and air-purging), and E736 cascade-communication faults on multi-unit installations (PCB firmware matching and DIP-switch master/follower configuration require Navien's service documentation). Heat-exchanger replacement, gas-valve adjustment, and any code that returns immediately after replacing the obvious sensor all indicate problems beyond simple component swap-out — board-level diagnosis or combustion-analyzer work requires the right tools and Navien service software. Navien Technical Support is reachable at 1-800-519-8794 for parts verification and dispatch.

Quick Answer

Navien (Kyungdong Navien — Korean) condensing tankless water heaters and combi-boilers — NPE-A (advanced), NPE-S (standard), NCB-E (combi), and NHB (hydronic) — display E-prefix three-digit fault codes (E001–E999) on the front-panel screen. The most-searched codes — E003 (ignition failure), E016 (heat-exchanger overheat), E046 (high-limit switch), E060 (dual venturi), E110 (air pressure), E432 (cold inlet 2 thermistor), E438 (combi circulation pump), and E515 (PCB communication) — cover combustion, sensor, pressure, pump, and controller faults across the residential and light-commercial range.

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By Octavian Ghindea

Co-founder & CTO · Reviewed May 2026

What error codes does Navien display?

E003

Ignition failure — gas, flame rod, igniter, venting, or ground

E012

Flame loss — clogged intake air filter, fouled flame rod, unstable gas pressure

E016

Heat-exchanger overheat — scale buildup or restricted water flow

E030

Exhaust overheating — scale, restricted flow, or vent partial blockage

E046

High-temperature limit control fault — wiring or failed limit switch

E060

Dual venturi limit switch fault — wiring, actuator, or PCB

E110

Air-pressure differential fault — vent, intake filter, or condensate trap

E432

Cold water inlet 2 thermistor open or short — dual-HX models

E438

Circulation pump abnormal operation — combi models only

E515

Internal PCB communication fault — subcode identifies failed peripheral

Common questions about Navien equipment

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