Turn off power → Press and hold SET + UP → Reapply power → release after 10s. Disclaimer : This article is a generic guide based on common Romstal solar controller logic. For the exact wiring diagram and firmware-specific functions, refer to the official Romstal Solar 24S manual included with your product or contact Romstal technical support. If you have a different Romstal Solar 24S product (e.g., a solar street light or inverter), please reply with a photo of the device or its label for a corrected manual.