The expansion vessel is a small tank that is used to protect closed systems from excessive pressure. The tank is filled with air that acts as a cushion against surges in pressure within the system.
This part is present in 45 different boilers in the Baxi range
![BAXI 5114691 EXPANSION VESSEL (8LTR) [4591]](http://allgasltd.com/cdn/shop/files/BAXI_5114691_EXPANSION_VESSEL.png?v=1682504235&width=1445)