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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.
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
Why South Shore homeowners choose Johnson Bros.
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.
Need help fast? Call for urgent plumbing issues. Booking online is best when you want the next open appointment without waiting on the phone.
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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 for urgent help now. Book online when you want the next available fit for your schedule.