Worcester Bosch 87161425050 Heatslave Expansion Vessel - 12L

The Worcester Bosch 87161425050 is a 12 litre expansion vessel used in Worcester Bosch oil-fired combi appliances. It sits on the sealed heating circuit and absorbs the volume increase as the system water heats, holding the pressure steady instead of letting it climb. Inside, a diaphragm separates the water side from a pre-charged air side, so the vessel acts as a buffer against expansion and contraction across the heating cycle.

• System pressure rises sharply once the appliance is running and the water heats up
• Pressure drops repeatedly and the system needs regular topping up
• Water discharges from the pressure relief valve during normal operation
• The vessel feels heavy or full of water when the system is drained, indicating a failed diaphragm
• Pressure swings between cold and hot states that cannot be settled by recharging the air side

• Check the appliance model and serial number against the compatibility list to confirm the 12 litre vessel is the correct fitment
• Confirm the part number on the existing vessel or in the appliance documentation, and cross-check the alternative numbers 1018309 and N7243
• Check whether a gasket or sealing washer is needed for the connection when the vessel is swapped
• This part is fitted to a gas appliance; installation must be carried out by a Gas Safe registered engineer.