Thermostat shows E9 and cannot detect external floor sensor in underfloor heating setup.

Safety first: Isolate power to the thermostat and underfloor heating manifold before working on wiring.

• Confirm sensor type: Ensure the installed floor sensor is a Drayton-compatible NTC with the correct resistance curve.
• Check connections: Remove the thermostat from the wall and verify that the floor sensor wires are firmly clamped in the designated sensor terminals.
• Test resistance: Disconnect the sensor and measure resistance with a multimeter. Compare to the expected value for the floor temperature. Infinite or near-zero readings indicate a faulty sensor or cable.
• Inspect conduit: If possible, check the sensor cable in the floor conduit for crushing or water ingress at the manifold end.
• Replace sensor: If faulty, install a new Drayton floor sensor in the existing conduit. Reconnect, restore power, and confirm that the thermostat now reads a floor temperature and E9 is cleared.