Thermostat shows E9 and refuses to operate heating due to detected over-temperature condition.

Safety first: Over-temperature can damage floors or pipes. Turn off the heating circuit at the main isolator until the cause is identified.

Steps to diagnose and fix:

• 1. Allow system to cool: Leave heating off for several hours and monitor actual room and floor temperature with an independent thermometer.
• 2. Check installation location: Ensure the thermostat is not mounted above radiators, towel rails, or in direct sunlight, which can cause false high readings. Relocate if necessary.
• 3. Verify floor sensor placement: For underfloor heating, confirm the sensor is positioned in the heated zone but not directly touching heating cables or pipes. If incorrectly placed, consider relocating using a conduit.
• 4. Review max temperature settings: In the thermostat menu, check the maximum floor and room temperature limits. Adjust to Danfoss-recommended values for your floor type (e.g., 27–29°C for wooden floors).
• 5. Test sensor accuracy: Measure the resistance of the floor sensor and compare to Danfoss NTC tables. A sensor reading too low (simulating high temperature) may be defective and require replacement.
• 6. Reset error: After correcting the cause, reset the thermostat or clear the alarm in the menu. Monitor operation to ensure E9 does not recur.

When to call a professional: If the floor has overheated or shows damage (warping, discolouration), consult a flooring specialist and heating installer.