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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.
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.
What causes 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.
What you can safely check first
- Note whether the water is genuinely the wrong temperature or only the display disagrees. Both happen with E027 and it is the first thing we ask.
- One reset is reasonable. If E027 returns immediately, the sensor or its wiring is the cause rather than a glitch.
When to stop and call us
The outlet sensor is accessible and replaceable in a normal service visit, but testing it against the board is meter work. E027 is usually one of the shorter Navien visits.
Seeing E027 on your Navien?
Book online and we will diagnose the actual cause, explain what we find, and price the repair before starting.
Navien 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 to send a licensed technician out, not charged at all if you approve 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.
Other codes on this unit? See all Navien error codes.
Why South Shore homeowners choose Johnson Bros.
Navien E027 diagnosed properly
We diagnose the cause rather than clearing the code and hoping. You get an upfront price before any work starts.
Not sure what's wrong? Send a photo or videoBooking online is the quickest way to hold the next open appointment. Call instead if it is urgent and you would rather talk to someone.
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Navien E027 diagnosed properly
We diagnose the cause rather than clearing the code and hoping. You get an upfront price before any work starts.
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