When you cleaned the drain pump you may have accidentally caused a wire connector to come loose, since you didn't have this error code before you cleaned the drain pump. I'd first start by checking all the wire connections to the CCU and User Interface.
F06 E02=COMMUNICATION ERROR UI TO CCU
Communication between Central Control Unit (CCU) and User Interface (UI) has not been detected.
• Verify continuity in cable between CCU (UI7) and UI (C2). See wiring diagrams.
• Check AC and DC supplies. See TEST #1 (CCU/Power Check).
• See TEST #2 (User Interface).