F16 error and thermostat cannot detect floor temperature in underfloor heating mode

Safety first: Isolate power to the thermostat before accessing terminals.

Steps:

• 1. Verify configuration: In the thermostat installer menu, confirm that 'Floor sensor' mode is enabled and the correct sensor type (e.g. 10k NTC) is selected.
• 2. Check connections: Remove the thermostat and inspect the floor sensor terminals. Tighten screws and ensure the cable is not nicked or crushed.
• 3. Measure resistance: With the sensor disconnected, measure resistance across the two sensor wires. Compare to Ideal's specification for the current floor temperature. Infinite or near‑zero resistance indicates a failed sensor or cable.
• 4. Replace accessible sensor: If the sensor is in a conduit, pull out and replace with a new Ideal‑compatible floor probe. If it is buried directly in screed without conduit, you may need to switch to air‑sensor control and limit maximum floor temperature via boiler controls.