Worcester Bosch 8738901137 Buderus Expansion Vessel 9L

The Buderus expansion vessel is a sealed diaphragm vessel supplied by Worcester Bosch under part number 8738901137. It holds a 9 litre charge of system water and gas, absorbing the expansion that occurs as the heating circuit warms up so that pressure stays within the working range of the appliance. It is a service component for Buderus-branded heating equipment and is identified on the trade side by the alternative number 1031616.

• System pressure climbs quickly once the boiler fires and drops again as it cools.
• The pressure relief valve discharges, leaving water from the discharge pipe.
• The boiler locks out or shuts down on low pressure even after topping up.
• The pressure gauge reads high on the cold fill and rises further when hot.
• Water is found at the Schrader valve on the vessel, indicating a split diaphragm.

• Confirm the appliance model and GC number, then match the part number 8738901137 against the vessel currently fitted.
• Check the capacity and connection arrangement of the existing vessel against this 9 litre unit before removal.
• Note the alternative numbers 1031616 and WB8738901137, as the same vessel may be listed under any of them.