Burner control indicates lockout due to internal fault, no start sequence, red light on immediately

Safety: Disconnect power at the breaker and verify no voltage is present before touching wiring.

Steps:

• Check supply voltage: Use a multimeter to confirm correct line voltage at the burner (typically 120V or 230V depending on model). Correct any wiring or breaker issues.
• Inspect connectors: Remove and reseat the multi-pin plug from the Riello control box. Look for corrosion, burning, or loose pins.
• Check for moisture: Inspect the control box and burner compartment for signs of water leaks or condensation. Correct any source of moisture.

If A05 persists and all external conditions are normal, the control box is likely defective and should be replaced with the exact Riello replacement part by a qualified technician.