Ariston gas water heater displays E05; unit attempts to ignite but fails, often with clicking sounds.

Safety first: Turn off gas and power before opening the unit. If you suspect a gas leak, do not attempt repairs yourself.

• Check gas supply: Verify the main gas valve to the heater is fully open. Confirm other gas appliances in the home are working to rule out supply issues.
• Inspect ignition electrode: Remove the front cover and locate the spark electrode. Check for cracks in the ceramic, carbon buildup, or corrosion on the tip. Clean gently and replace if damaged.
• Verify electrode gap: Ensure the electrode tip is at the correct distance from the burner surface (refer to Ariston service manual; typically 3–5 mm). Adjust carefully if needed.
• Check wiring and ground: Ensure the ignition cable is firmly connected and not arcing to the chassis. Confirm the appliance has a good earth/ground connection.

If the unit still shows E05 after cleaning and verifying gas supply, the ignition transformer or control board may be defective. This should be tested and replaced by a qualified gas technician.