Navien furnace displays E046, unit may run at reduced capacity or shut down

Safety: Turn off power before working on low-voltage wiring.

• Locate outdoor sensor: The Navien outdoor temperature sensor is typically mounted on an exterior north-facing wall away from direct sunlight and other heat sources. Verify it is securely mounted and not physically damaged.
• Inspect wiring: Follow the two-conductor cable from the sensor back to the Navien furnace. Look for cuts, staples through the cable, or corrosion at connection points. Repair or replace damaged cable.
• Check connections at PCB: Ensure the sensor wires are landed on the correct terminals and are tight. Remove and reinsert if necessary to clean contacts.
• Measure sensor resistance: Disconnect the sensor and measure resistance with a multimeter. Compare to Navien's temperature-resistance chart. Replace the sensor if readings are out of range.
• Reset and verify: Restore power, reset the unit, and confirm that the displayed outdoor temperature is reasonable. If E046 persists with a known-good sensor, the PCB input may be defective and require replacement.