The Zip Hydroboil expansion vessel and check valve may be needed if your nearest cold water draw off from the unit is within 4 feet. Basically the expansion vessel allows for the expansion and contraction of the heated water within the tank.
For use with the zip aquapoint water heaters
Includes check valve
15 mm x 12.7 mm BSP connections
3.5 bar
Technical specification
ShapeCylinderPre Charge Bar Rating3.5 barModelAQ2Height250 mmDiameter150 mmConnections15 mm x 12.7 mm in BSPCapacity2 LManufacturer Model NoAQ2Brand NameZip