If your washer is making a buzzing sound when pressing the start button and displaying an F11 error code, this typically indicates a communication problem between the Central Control Unit (CCU) and the Motor Control Unit (MCU). Although you've checked the CCU and found it to be clean and free from burn marks, the issue might not be visibly apparent.
First, ensure that all wiring connections between the CCU and MCU are secure, as loose or damaged wires can cause communication errors. Also, inspect the MCU for any signs of damage or loose connections. It's a good idea to power cycle the washer by unplugging it for a few minutes and then plugging it back in, which can sometimes reset the system and clear temporary glitches.
Despite the CCU appearing fine, there's a possibility that an internal component is malfunctioning, and the same could be true for the MCU. If you're not comfortable checking these components or if the problem persists, consider calling a professional technician for a more thorough diagnostic and to determine if any parts need replacing.
Remember, safety is paramount when working on appliances. Always ensure the machine is unplugged before inspecting any internal components, and if you're unsure or uncomfortable with these steps, it's safer to consult with a professional technician.