Worcester Bosch Expansion Vessel 12 Litre 87161083890

The Worcester Bosch 87161083890 is a 12 litre expansion vessel used within Worcester Bosch combi and oil-fired boiler installations. An internal diaphragm separates a sealed air charge from the system water, so the vessel can absorb the volume increase as the water heats without pushing system pressure beyond its working range. Keeping that pressure stable protects the boiler's seals, heat exchanger and pressure relief valve from repeated stress.

• System pressure climbs quickly once the boiler fires and falls back again as it cools.
• Boiler pressure drops repeatedly and the filling loop is used regularly to top up.
• Water discharges from the pressure relief valve during heat-up.
• The vessel feels heavy or sounds full of water when tapped, rather than hollow.
• The air charge cannot be held at the vessel valve, or water escapes when the charge is checked.

• Check the boiler model and serial number against the compatibility list before ordering.
• Confirm the number on the existing vessel; 1020423 and BS49010 have both been used for this item.
• Check whether a new gasket or sealing washer is needed for the connection while the vessel is off.
• This part is fitted to a gas appliance; installation must be carried out by a Gas Safe registered engineer.