Baxi Expansion Vessel 5114691 (8L)

Genuine Baxi OEM expansion vessel for sealed heating systems. The vessel absorbs water expansion on heat-up to maintain safe, stable pressure and protect boiler components.

• Manufacturer: Baxi
• Part type: Expansion vessel (sealed system)
• Capacity: 8 litres
• MPN: 5114691
• GTIN / EAN: 5039177659815

Compatible ranges (examples)

Used across many Baxi Group appliances (model/year dependent), including:

• Baxi: Duo-tec / Duo-tec ErP, Megaflo / Megaflo ErP, Platinum / Platinum+ / Platinum ErP, Gold / Gold ErP, Heatmax, Promax / Promax ErP, Titanium / Titanium ErP
• Main: Eco, Eco Elite, Eco Elite ErP
• Other families: Apollo, System IE, and related variants

Always confirm against your boilers data plate or parts list for MPN 5114691.

What this part does

The vessel contains an air charge separated from system water by a membrane. As water expands, the vessel cushions the pressure rise, reducing PRV discharge and protecting the system.

When to replace

• Frequent pressure loss or PRV dripping
• Rapid pressure rise on heat-up
• Vessel fails to hold pre-charge (membrane failure)

What’s in the box

• 1 Baxi expansion vessel 5114691 (8L)

Installation & safety

Must be fitted and pre-charged by a qualified Gas Safe engineer. After installation, set the vessel pre-charge to manufacturer guidance and verify system pressure and operation.