Worcester Bosch Mini Expansion Vessel HA50 87161425030

The HA50 mini expansion vessel is a Worcester Bosch spare that absorbs the pressure rise created as the water in a sealed heating system heats up. It sits inside the boiler casing and provides the air cushion that keeps system pressure stable through the heating cycle. This is the vessel used across the Worcester 24i and 28i RSF combi and natural gas range.

• System pressure climbs quickly once the boiler fires and drops again as it cools
• The pressure relief valve discharges water, often onto the wall or out of the discharge pipe
• Boiler locks out or shows a low pressure fault even after topping the system up
• Water or moisture appears at the vessel charge valve when the Schrader valve is depressed
• The vessel feels heavy or gives no resistance when tapped, indicating a failed internal diaphragm

• Confirm the GC number on the appliance data badge against the compatibility list, as the 24i RSF was produced in more than one build.
• Check the previous number ZMMIS038 and the alternative numbers 1018305, N7391 and WB87161425030 against the part you are removing.
• Inspect the vessel connection and any sealing washer on removal, as these are often reused and can weep if disturbed.
• This part is fitted to a gas appliance; installation must be carried out by a Gas Safe registered engineer.