Ariston water heater does not power on; no lights or display.

Safety first: Before opening the unit, turn off the breaker and verify absence of voltage.

• Check breaker and fuses: Reset the breaker and replace any blown fuses with correct ratings. If they trip again, investigate further before resetting.
• Verify supply voltage: Measure voltage at the heater's terminal block. If no voltage, trace back to the distribution panel.
• Inspect internal connections: Ensure the power switch (if present) is ON and that all internal connectors are firmly seated.
• Check thermal fuse (if accessible): Some Ariston models have a non-resettable thermal fuse on the board. If open, the board usually must be replaced.