F3 displayed and thermostat does not detect room temperature correctly

Safety first: Turn off power to the thermostat if it is hard‑wired. For battery models, remove batteries before opening the casing.

Steps to check:

• 1. Compare displayed temperature: Place a reliable thermometer near the thermostat. If the thermostat shows dashes, F3, or an obviously wrong value (e.g. -20°C), the sensor is likely open circuit.
• 2. Inspect for physical damage: Remove the thermostat from the wall and open the housing (if user‑serviceable). Look for cracked PCB, corrosion, or water damage around the small NTC sensor (usually near the air vents).
• 3. Check external sensor (if fitted): If your Ideal smart thermostat uses a remote room sensor, inspect the sensor cable and terminal connections. Tighten loose screws and ensure polarity (if applicable) is correct. Test continuity of the sensor cable.
• 4. Reset and update firmware: Reassemble, restore power, and perform a factory reset from the settings menu. Check for firmware updates via the Ideal app; install if available and re‑test.

Note: The internal NTC sensor is usually not user‑replaceable; the entire thermostat head is typically replaced.