Thermostat shows F02 and ignores temperature changes; may default to frost protection mode.

Safety first: External sensors are low‑voltage but may be routed near mains cables. Isolate boiler and thermostat receiver before working on wiring.

• Identify the sensor:
  • Check your installation manual to confirm if a remote room sensor or outdoor sensor is connected to the Ferroli thermostat.
• Inspect wiring:
  • Locate the sensor terminals on the thermostat base or receiver (often marked as NTC, EXT, or OUT).
  • Check that the two‑core cable is intact, not crushed, and firmly clamped.
  • Repair or replace any visibly damaged cable.
• Check sensor resistance (for advanced DIYers with a multimeter):
  • Disconnect the sensor from the terminals.
  • Measure resistance across the sensor leads; typical Ferroli NTC sensors are in the 5–15 kΩ range at room temperature (consult manual).
  • If reading is infinite (open) or near 0 Ω (short), replace the sensor.
• Disable external sensor (temporary workaround):
  • If allowed by the thermostat menu, disable the external sensor input so the thermostat uses its internal sensor only.
• Replace faulty sensor:
  • Install a compatible Ferroli outdoor/remote NTC sensor and clear the F02 error.