Display shows A08; unit may run briefly then shut down, or may not start at all.

Safety: Isolate electrical power before working on internal wiring.

Steps:

• Locate return NTC: Typically mounted on the return pipe entering the heat exchanger or hydraulic block.
• Inspect connector: Disconnect and reconnect the NTC plug to clean contacts. Check for bent pins or corrosion.
• Check cable routing: Ensure the cable is not pinched or damaged by the casing or other components.
• Reset: Restore power and reset the furnace. If A08 persists, the sensor is likely faulty.

Professional help: Replacement of the NTC and verification of correct resistance values should be done by a technician.