Display shows E08; furnace may run at reduced output or shut down.

Safety: Turn off power before removing sensor connectors.

• Locate the return sensor: The return NTC is typically mounted on the return pipe entering the heat exchanger.
• Check physical condition: Inspect the sensor body and cable for cracks, swelling, or signs of water damage.
• Verify connections: Reseat the connector on the PCB and ensure the cable is not pinched by panels.
• Test and replace: If you can measure resistance, compare with the Kospel NTC chart. Replace the sensor if readings are out of range.

After replacement, restore power and confirm that the E08 code clears and temperatures display correctly.