F05 error, unit may start but then shut down with no obvious temperature issue.

Safety: Isolate power before working on sensors.

• 1. Compare sensors: With the unit cold, flow and return NTCs should read similar temperatures. Large differences suggest a faulty sensor or poor contact.
• 2. Refix sensor: Ensure the return NTC is firmly clipped to the pipe and insulated from ambient air.
• 3. Replace NTC: If in doubt, replace the return NTC with a genuine Ferroli part.