Vaillant Automatic Air Vent Ecotec Efit VU VAILLANT104521

The Vaillant 104521 is an automatic air vent supplied by Vaillant for use in its Ecotec, Efit and VU appliance families. It sits on the heating circuit and continuously bleeds off the small quantities of air that collect as water is heated and circulated, allowing the system to run without trapped pockets of gas.

Because the vent works automatically, it removes the need for manual bleeding at that point on the appliance. The part is listed under Vaillant boiler spares and carries the manufacturer code 104521.

• Water weeping or dripping from the vent body or its cap
• Boiler pressure falling repeatedly with no visible leak elsewhere on the system
• Gurgling, kettling or rushing noises from the appliance as air passes through the heat exchanger
• Radiators needing to be bled far more often than usual
• Air-related lockout or ignition faults that return shortly after the system is bled

• Check the boiler's data badge and confirm the model falls within the Ecotec, Efit or VU ranges
• Match the manufacturer code 104521 against the number printed on the existing vent
• Inspect the sealing washer or O-ring at the vent connection and replace it if it is hardened or flattened
• Work on the appliance should be carried out by a competent person, with the system isolated and depressurised first