E4 error and thermostat indicates that maximum floor temperature limit has been exceeded.

Safety: Overheated floors can be a fire and scalding hazard. Turn off heating immediately if floor feels excessively hot.

• Step 1 – Turn off underfloor heating:
  • Switch the thermostat to OFF or set a very low setpoint.
• Step 2 – Check floor temperature:
  • Use an infrared thermometer to measure floor surface temperature.
  • If it is within safe range (typically <29–35°C depending on floor type), the sensor may be misreading.
• Step 3 – Verify settings:
  • In installer menu, check Max floor temperature setting.
  • Adjust to manufacturer-recommended value for your floor covering.
• Step 4 – Inspect floor sensor:
  • If readings are clearly wrong, test the sensor resistance and replace if necessary (see F2/F3 procedures).
• Step 5 – Check valves and actuators:
  • Ensure underfloor heating actuators close properly when there is no heat demand.
  • Replace any stuck actuators.