Thermostat shows F6 and cannot detect external room sensor when configured to use one.

Safety: Turn off power to the thermostat circuit before working on low-voltage wiring.

• Step 1 – Confirm configuration:
  • In the installer menu, verify that External room sensor is enabled only if one is actually installed.
  • If no external sensor is present, disable this option to clear F6.
• Step 2 – Inspect sensor wiring:
  • Remove thermostat from wall plate.
  • Check that both wires from the external sensor are firmly connected to the correct sensor terminals.
  • Tighten any loose screws.
• Step 3 – Measure sensor resistance:
  • Disconnect the sensor wires from the thermostat.
  • Measure resistance across the two wires with a multimeter.
  • Compare reading to Protherm sensor specification (e.g. 10k NTC at 25°C).
  • If the meter shows open circuit, the sensor or cable is broken.
• Step 4 – Replace sensor if faulty:
  • Install a new Protherm external room NTC sensor.
  • Route the cable away from mains wiring and moisture sources.
  • Reconnect to thermostat and secure.
• Step 5 – Test operation:
  • Restore power and verify that F6 is cleared and room temperature is displayed correctly.