Furnace displays E15, unit may continue to run at reduced performance.

Safety: Turn off power before accessing sensor wiring.

Steps:

• Locate outdoor sensor: Find the small sensor mounted on an exterior wall, away from direct sunlight and heat sources.
• Inspect cable and connections: Check for weather damage, loose terminals, or corrosion at junction boxes.
• Replace sensor if needed: If the sensor body is cracked or readings are clearly wrong (e.g., showing extreme temperatures), replace it with a Cointra-compatible outdoor NTC.

Professional service: If a new sensor does not resolve E15, the control board may have a defective sensor input.