Hi there,
For troubleshooting the Siemens HI921, start by checking the power supply to ensure it’s stable and within the recommended voltage range. Next, inspect the wiring connections to ensure they are secure and properly terminated. If the unit is displaying error codes, consult the manual to identify the specific issue. Additionally, make sure the sensors are clean and free of any obstructions. If the problem persists, consider contacting Siemens technical support for further assistance.