Display shows E127; unit may not respond correctly to temperature settings.

Safety: Turn OFF power before working on wiring.

Steps:

• 1. Locate outdoor sensor: Find the Navien outdoor temperature sensor mounted outside. Ensure it is not directly in sunlight or near heat sources.
• 2. Inspect cable: Check the cable from the sensor to the unit for cuts, staples through the wire, or weather damage.
• 3. Reseat connections: At the unit, ensure the outdoor sensor wires are firmly connected to the correct terminals.

If E127 remains, the sensor is likely defective and should be replaced. Use a Navien-compatible outdoor sensor.