Ariston 406801 Kit A - 2 Litre Expansion Vessel With 15 mm Single Check Valve

The Ariston 406801 kit pairs a 2 litre expansion vessel with a non-return valve, supplied for Ariston Andris and Lux water heaters. The vessel takes up the volume increase as stored water heats and expands, holding system pressure steady instead of letting it climb. The non-return valve stops heated water from travelling back down the cold supply.

• The pressure relief valve discharges during heat-up, with water appearing at the tundish or discharge pipe
• System pressure climbs sharply as the cylinder warms and drops again once it cools
• Water weeps from the vessel's air valve, or the shell shows corrosion or pitting
• The air charge is lost repeatedly, so the vessel needs re-pressurising again within weeks
• Warm water is found in the cold inlet pipework, indicating the non-return valve is passing

• Read the model and serial number from the heater's rating plate and match it to the compatibility list
• Compare the existing component against part number 406801 to confirm the correct kit
• Check whether a new gasket or sealing washer is needed at the connection before fitting
• This is not a gas-carrying component