F8 error: domestic hot water temperature reading is erratic or implausible.

Safety first: Turn off power and close water valves if removing sensors from wet parts.

Steps:

• Locate DHW NTC: Typically mounted on or near the hot water outlet pipe inside the heater.
• Check connection: Reseat the connector on the sensor and on the PCB. Clean any oxidation from contacts.
• Inspect for scale: If the sensor is in a pocket or well, heavy scale can insulate it. A professional descaling of the DHW circuit may be required.
• Replace sensor: If the error persists, replace the DHW NTC with an original Saunier Duval part.

Warning: Ensure the system is depressurized before removing any sensor that is in direct contact with water.