Sure, for troubleshooting the Siemens FDT421, the first thing you should do is check the error code displayed on the panel. Once you have the error code, consult the user manual or technical documentation provided by Siemens. Typically, error codes are accompanied by specific instructions or recommended actions to resolve the issue. If you’re unable to find a solution in the documentation, you may need to contact Siemens technical support or a certified technician for further assistance. Additionally, make sure to inspect the system for any visible signs of damage or malfunction, such as loose connections or faulty components. If you can provide more details about the error message you’re seeing, I may be able to offer more specific advice.