Thermostat displays E3 and heating output is disabled; device may feel unusually warm to the touch.

Safety first: Switch off power to the thermostat and connected heating equipment at the breaker. Allow the thermostat to cool for at least 10–15 minutes.

Steps to resolve:

• Check load rating: Confirm the connected heating load (e.g., electric underfloor mat, boiler control, valve actuators) does not exceed the thermostat's maximum current rating (typically 3–16 A depending on model). If the load is too high, install a suitable contactor/relay and use the thermostat only as a control signal.
• Inspect installation location: Ensure the thermostat is not installed directly above radiators, towel warmers, or in a recessed box with poor airflow. Relocate if necessary to a cooler, ventilated wall surface.
• Check wiring tightness: Remove the thermostat and inspect terminal screws. Loose connections can cause localized heating. Tighten all terminal screws to manufacturer torque specs.
• Ventilation: Make sure front and side vents are not blocked by paint, wallpaper, or furniture. Clear any obstructions.

After adjustments: Restore power and monitor operation. If E3 recurs quickly under normal load and proper installation, the internal thermal sensor or relay assembly may be damaged and the thermostat should be replaced.