Thermostat shows F7 and cannot detect external temperature for weather-compensated control

Safety: Turn off power to the boiler before accessing its terminals. Outdoor sensor wiring is low voltage but runs through the boiler casing.

• Check configuration: In the thermostat menu, ensure that an external sensor is enabled only if one is actually installed. Disable it if you do not have an outdoor sensor.
• Inspect sensor wiring: Locate the outdoor sensor terminals on the boiler or external junction box. Check that the two-core cable is firmly connected and not damaged outside.
• Measure resistance: With power off, disconnect the sensor and measure its resistance with a multimeter. Compare with the Saunier Duval sensor table (typically several kΩ at room temperature). Infinite or near-zero resistance indicates a faulty sensor.
• Check for shorts: Inspect the cable route for crushed or water-damaged sections that could short the cores.

Replace the outdoor sensor if readings are out of range or wiring is damaged.