Thermostat displays E20 and room temperature swings widely around setpoint

Safety first: No special hazards; this is a comfort and efficiency issue.

• Check location: Ensure the thermostat is mounted on an internal wall, about 1.5 m above floor level, away from radiators, direct sunlight, and draughts.
• Adjust calibration: In the thermostat settings, use the temperature offset/calibration function to align the displayed temperature with a reliable thermometer.
• Change control mode: If using simple on/off control, try enabling TPI (time proportional integral) or OpenTherm modulation if supported by your boiler to reduce overshoot.
• Update firmware: Connect to Wi‑Fi and check for firmware updates that may improve control behaviour.
• If E20 persists with large swings: The internal sensor or control logic may be faulty. Consider replacing the thermostat.