Navien · Tankless Water Heater Moderate

E027 — Navien Tankless E027 — Sensor Abnormality

E027 indicates a sensor abnormality. Depending on the model it is the return-temperature sensor (combi/boiler units) or an air-pressure / flow sensor (CH-240 / NPE) reading out of range. Confirm the specific sensor for your model — it is not a gas-type / dip-switch configuration fault.

Keep using it?
Yes, with caution
DIY difficulty
Easy
Verified against
navieninc.com ↗

How to fix it

  1. Identify the specific E027 sensor for your exact Navien model in the service manual.
  2. Inspect that sensor and its wiring/connector.
  3. Test or replace the sensor if out of range; have Navien service diagnose if unclear.

Why it happens

Typical signs: E027 shown on the control · Unit stops heating / shuts down · May clear on reset and recur

  • A temperature, air-pressure, or flow sensor is reading out of range The exact sensor depends on the model — return-temp sensor on combi/boiler units, air-pressure or flow sensor on others.
  • Wiring or connector fault to the affected sensor Check the harness/connector for the sensor named for your model.

More Navien tankless water heater codes

E003 E003 — Ignition Failure E003C E003C — Cascade Ignition Failure E012 E012 — False Flame / Flame Loss E016 E016 — Overheat / High-Limit Trip E030 E030 — Abnormal Exhaust Temperature (Flue Overheat) E046 E046 — Abnormality in Limit Control (Heat-Exchanger High-Limit)

All Navien codes → All tankless water heater codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: navieninc.com.