Navien Expansion Vessel 12L 30022587A

The Navien 12L expansion vessel (part number 30022587A) is a sealed diaphragm vessel used in the heating circuit of Navien LCB 700 boilers. It absorbs the volume increase of water as the system heats up, limiting pressure rise and protecting components from excessive stress. It is fitted across the LCB 700 combi and system range in both internal and external variants.

• System pressure rises sharply when the boiler heats up and falls again as it cools
• Boiler pressure drops repeatedly and needs frequent topping up
• Water discharging from the pressure relief valve during normal operation
• Water or corrosion visible at the vessel connection or on the vessel body
• Pressure gauge reading fluctuates widely across the heating cycle

• Confirm your boiler model against the LCB 700 range listed above
• Check whether your appliance is the internal or external variant
• Verify the existing vessel is rated at 12 litres before ordering
• Check access to the vessel and its connection point before starting work