Ariston gas water heater shows E06 and shuts down during operation; water may suddenly go cold.

Safety first: Turn off gas and power. Do not operate the heater with a suspected flue blockage—risk of carbon monoxide.

• Inspect flue terminal: From outside, check that the flue outlet is not blocked by debris, nests, snow, or vegetation. Clear any obstructions.
• Check air intake (room-sealed models): Ensure the concentric flue air intake is not obstructed and that the appliance has adequate ventilation.
• Inspect flue gas sensor: Remove the front cover and locate the flue gas temperature sensor (usually clipped to the flue hood). Check wiring and connector. If the sensor is cracked or sooted, replace it with an Ariston-compatible part.
• Verify fan operation: On models with a fan, listen for fan start-up. If the fan does not run or is noisy, it may be failing and causing overheating. Fan replacement should be done by a technician.

After clearing obstructions and checking the sensor, restore gas and power and test. Persistent E06 requires professional combustion and flue analysis.