B

A 1021 error can only be cleared by powering the appliance off and back on again the hot water sensor has been changed if open or short circuit, or refitted to the pipe if it has fallen off.
▶ Check the domestic hot water temperature sensor is connected and the harness is fitted securely to the sensor.
▶ Check the resistance of the temperature sensor and replace if required.
▶ Check the continuity of harness and replace if required.