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    Johnson Bros. Plumbing & Drain Cleaning
    Error Code E027

    Navien E027 — Outlet Water Temperature Sensor

    The sensor that tells the Navien how hot the water leaving the unit is — it's not reporting correctly. Usually a sensor replacement or wiring fix.

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    4.8 stars on Google · 367 reviews across Quincy and AbingtonMA Lic. PL #17034-MQuincy & Abington offices

    What E027 Means

    The outlet water temperature sensor is how your Navien knows how hot the water is after it leaves the heat exchanger. That reading feeds back to the control board, which uses it to modulate the burner and hit your setpoint. If the sensor reports an impossible value (open circuit, short, or wildly out of range), the unit can't trust it, so it locks out and posts E027.

    Good news: E027 is one of the simpler faults to diagnose and fix. It's almost always a sensor, wiring, or connector issue — not a deep combustion or gas problem.

    Common Causes of E027

    1. Failed outlet temp sensor

    The dominant cause. The sensor is a wear part; after years of thermal cycling it can drift or fail outright. Direct replacement.

    2. Wiring corrosion or damage

    Wiring between sensor and control board can corrode, pinch, or break, especially near the sensor itself where it sees heat and humidity.

    3. Connector issues

    Corroded or loose connector at the control board. Often a quick fix once identified.

    4. Control board fault

    Less common but possible — the board misreads a good sensor. We test sensor integrity before condemning the board.

    E027 FAQs

    What does Navien error code E027 mean?
    E027 is an outlet water temperature sensor fault. The sensor that measures the temperature of water leaving the heat exchanger is reporting an out-of-range value — either open circuit (broken wire or disconnected sensor) or short circuit (wiring issue or failed sensor). The unit safes itself because it can't reliably control outlet temperature without that reading.
    What causes E027?
    Most common: (1) the sensor itself has failed — they're a wear part that can fail after years of thermal cycling; (2) wiring from the sensor to the control board is corroded, pinched, or disconnected; (3) a connector on the control board side is loose or corroded; (4) less commonly, a control board fault that misreads the sensor. The sensor is the first thing we check because it's by far the most common failure.
    How hard is E027 to fix?
    It's one of the simpler Navien error codes to diagnose and resolve. The outlet temp sensor is accessible and replaceable in a typical service visit. Wiring fixes take a few more minutes. Board-level issues are rarer but we test for them. Compared to E003 or E012, E027 is usually a shorter visit.
    How much does E027 repair cost?
    Our standard $99 service fee applies toward the repair. The sensor itself is a relatively low-cost part. If the issue is wiring or a connector, labor is the main cost. We give you an upfront price before work starts.
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    Why South Shore homeowners choose Johnson Bros.

    Family-owned and local
    Serving Quincy, Abington, and the South Shore.
    Licensed and insured
    MA Master Plumber License PL #17034-M with insured work and professional standards.
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    We'll review your request and confirm the next available appointment.

    Navien showing E027? Usually a quick fix.

    Most E027s are a sensor or wiring repair — shorter visit than most Navien faults. Call us with the model number.

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    Areas we serve
    QuincyBraintreeWeymouthHinghamPlymouthMarshfieldScituateAbington

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    Navien showing E027? Usually a quick fix.

    Most E027s are a sensor or wiring repair — shorter visit than most Navien faults. Call us with the model number.

    Call About E027Book a Diagnostic

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