Vaillant Expansion Vessel 0020210628

The Vaillant 0020210628 is an expansion vessel used in Vaillant VWF and Flexotherm VWF heat pump appliances. It absorbs the expansion of water as it heats, holding system pressure within a stable range and protecting the circuit from excessive pressure rise. It is a serviceable component, so it can be replaced when the internal membrane or the vessel body fails.

• System pressure rises sharply when the appliance heats up and falls again once it cools.
• The pressure relief valve discharges water during normal heating cycles.
• The appliance repeatedly loses pressure and needs frequent topping up.
• Water is present at the vessel's air valve, indicating a split or perished membrane.
• Visible corrosion, weeping or staining around the vessel body or its connection.

• Confirm your appliance model against the fitment list above, including whether it is a standard VWF or a Flexotherm VWF variant.
• Check the part number on the existing vessel or in the manufacturer's parts list for your model.
• Inspect the vessel connection and mounting arrangement on your appliance before removal.
• Check the system pressure and relief valve operation first, as symptoms can also come from other parts of the circuit.