Baxi 720759301 Potterton 6L Expansion Vessel

The Baxi 720759301 is a 6 litre expansion vessel used in Baxi N/Tec heating appliances. It is a sealed tank divided internally so that a charge of air sits against the system water, absorbing the expansion that occurs as the appliance heats up and holding the circuit pressure within safe limits. Without a working vessel, the pressure in a sealed system swings sharply between cold and hot states.

• System pressure climbs quickly as the appliance heats and falls again once it cools.
• The pressure relief valve discharges water, or the appliance repeatedly locks out on low pressure.
• Water is found at the vessel's air valve when the Schrader valve is depressed, indicating a split diaphragm.
• The vessel feels heavy or full of water when removed, rather than light and hollow.
• Pressure has to be topped up frequently from the filling loop to keep the appliance running.

• Confirm the part number 720759301 against the label on the existing vessel or the appliance's parts list.
• Check the model and GC number on the appliance data badge, as Baxi used more than one vessel across its ranges.
• Allow for a new sealing washer or connection gasket if the existing one is compressed or damaged on removal.