Display shows L0, furnace does not respond, screen may be dim

Safety first: Switch off the appliance before checking electrical connections.

• 1. Measure mains voltage: Using a multimeter, verify that the supply voltage at the furnace terminals is within the range specified by Junkers (typically 220–240 V AC). If low, contact an electrician or utility provider.
• 2. Check power cable and plug: Inspect for damage, overheating, or loose terminals. Tighten and repair as necessary.
• 3. Dedicated circuit: Ensure the furnace is on a dedicated circuit and not sharing with high-load appliances that could cause voltage drops.
• 4. PCB power supply: If mains voltage is correct but L0 persists, the internal power supply on the control board may be defective and require replacement by a technician.