Thermostat shows E4 and heating output is disabled

Safety first: Switch off power to the heating circuit at the breaker. Allow the floor and thermostat to cool down.

Steps to troubleshoot E4 (overtemperature):

• 1. Allow system to cool:
  • Wait until the floor and thermostat feel at normal room temperature.
  • Do not cover the thermostat or floor sensor area with rugs or insulation.
• 2. Check floor temperature limit settings:
  • Power the thermostat back on.
  • Enter the configuration menu or use the Fibaro app.
  • Verify the maximum floor temperature limit (e.g., 27–35°C) is set correctly for your floor type.
  • Reduce the limit if it is set too high for wooden or vinyl floors.
• 3. Verify sensor accuracy:
  • Compare the displayed floor temperature with an external thermometer or IR thermometer.
  • If the reading is clearly wrong (e.g., shows 50°C but floor is cool), the floor sensor may be faulty.
• 4. Inspect relay operation:
  • With power off, remove the thermostat and inspect the relay area on the PCB for signs of burning or welded contacts.
  • If the relay is stuck closed, the heating may stay on continuously, causing overtemperature.
• 5. Replace faulty components:
  • If the floor sensor is inaccurate, replace it with a compatible Fibaro NTC sensor.
  • If the relay appears damaged or stuck, the thermostat unit should be replaced.

When to call a professional: Overheating can damage floor coverings and wiring. If E4 recurs frequently or you suspect a stuck relay or wiring fault, contact a qualified electrician or heating installer.