U9 displayed intermittently, furnace may continue to operate with reduced performance

Safety first: Isolate power before opening the control panel.

• 1. Access control panel: Remove the front cover and carefully open the control panel according to Junkers instructions.
• 2. Check ribbon cable: Ensure the flat cable between the display board and main PCB is fully seated at both ends. Reseat it if necessary.
• 3. Clean connectors: Use electrical contact cleaner on the connectors if signs of oxidation are present.
• 4. Inspect for damage: Look for cracks or burn marks on the display board. Replace the user interface module if defective.
• 5. EMI sources: Avoid routing high-voltage or motor cables close to the control wiring to reduce interference.