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    Johnson Bros. Plumbing & Drain Cleaning

    Navien Error Codes — What They Mean & What to Do

    Your Navien is giving you a code on purpose. It's telling you something specific. Clearing the code without fixing the cause will put you back here next month.

    Johnson Bros. — licensed MA master plumber, Navien service specialist. Quincy & Abington offices.

    Call (617) 479-9911Book Diagnostic
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    Common Navien Error Codes

    Quick reference — what each code points to. Click the highlighted codes for deeper dives.

    E003
    Ignition failure

    Most common startup fault. Gas valve, flame rod, venting, or low gas pressure.

    E004
    False flame detection

    Flame detected when it should not be. Usually a flame rod or ignition module issue.

    E012
    Flame loss during operation

    Unit ignited but lost flame. Flame rod, gas pressure, or combustion air.

    E016
    High exhaust temperature

    Scale buildup or reduced water flow through the heat exchanger. Usually a descale.

    E027
    Outlet water temp sensor

    Sensor or wiring fault. Straightforward diagnostic and part replacement.

    E030
    Exhaust temperature sensor

    Exhaust sensor fault. Replace sensor, verify venting.

    E040
    Gas pressure / supply

    Low supply pressure. Often a gas-line sizing issue, not a unit failure.

    E046
    Flow rate abnormally low

    Inlet filter clog, scale restriction, or valve issue.

    E109
    Fan / combustion blower

    Blower motor, RPM sensor, or wiring.

    A012
    Air intake fault

    Venting obstruction, damper, or pressure switch.

    E515
    Communication / PCB

    Control board communication fault. Often a wiring or board issue.

    E760
    Recirculation pump

    Internal recirc pump or sensor (NPE-A2 models with built-in recirc).

    How to Read Your Navien Display

    1. 1. Look at the front panel. The error code shows as an "E" followed by a 3-digit number (e.g., E003). Some codes start with "A" for air or "P" for pump.
    2. 2. Write it down exactly. "E003" vs "E030" point to very different issues.
    3. 3. Note the conditions: did it error on startup, during a shower, after a long idle, during a freeze? Context matters.
    4. 4. One reset attempt is fine — power off at the disconnect, wait 30 seconds, power back on. If it clears and stays clear, great. If it comes back, stop resetting and call.
    5. 5. Call (617) 479-9911 with the code and context. We'll tell you whether this is a same-day call or a standard-schedule diagnostic.

    Common Questions About Navien Error Codes

    What should I do when my Navien throws an error code?
    First, write down the exact code on the display (E003, E012, etc). Second, check the gas valve on the unit is open, the power is on, and there's no obvious issue (blocked vent outside, water leak underneath). Third, you can try a single power-cycle reset — turn the unit off at the disconnect, wait 30 seconds, turn it back on. If the code comes back, call us at (617) 479-9911. Don't keep resetting a unit that's locking out — the unit is telling you something specific.
    Are all Navien error codes covered by the warranty?
    The warranty covers parts failure. It does NOT cover issues caused by improper installation (wrong gas sizing, wrong venting), lack of maintenance (never descaled, scale-ruined heat exchanger), or external issues (low gas pressure from the utility side, blocked vent termination). The first step in a warranty service call is almost always a diagnostic to confirm what failed and why.
    Why does my Navien keep throwing the same code?
    Because the underlying cause hasn't been fixed — only the code was cleared. Error codes are symptoms. If E003 (ignition failure) keeps coming back after a reset, the gas valve, flame rod, venting, or gas pressure is still wrong. Clearing the code doesn't fix anything on its own.
    Is an error code always an emergency?
    No — most error codes put the unit in a safe lockout state. It stops working, but it is not dangerous. The exception is anything involving a gas smell, visible water leak, or CO detector activation. Those are emergencies — evacuate, call 911 or the gas utility, then call us. For a simple code lockout with no gas/water/CO issue, a next-business-day service call is appropriate.
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    We'll review your request and confirm the next available appointment.

    Your Navien has an error code — what's next?

    Tell us the code and what the unit is doing. We'll triage and tell you whether it's an emergency, a same-day call, or a scheduled diagnostic.

    Call About a Navien CodeBook a Diagnostic

    Need help fast? Call for urgent plumbing issues. Booking online is best when you want the next open appointment without waiting on the phone.

    Areas we serve
    QuincyBraintreeWeymouthHinghamPlymouthMarshfieldScituateAbington

    Related services

    Navien Service & Repair

    Main Navien service and maintenance page.

    Navien Installation

    Proper install — the #1 prevention for future error codes.

    Navien Overview

    Models, specialty, and service areas.

    Your Navien has an error code — what's next?

    Tell us the code and what the unit is doing. We'll triage and tell you whether it's an emergency, a same-day call, or a scheduled diagnostic.

    Call About a Navien CodeBook a Diagnostic

    Call for urgent help now. Book online when you want the next available fit for your schedule.