Baxi Expansion Vessel 8L 7875809

The Baxi 7875809 is an 8 litre expansion vessel supplied with a gasket. It is fitted to Baxi Aquaheat Hi and HWI appliances, where it absorbs the volume increase of water as the system heats and contracts again on cooling. This keeps system pressure stable and protects components such as the pressure relief valve from repeated discharge.

• System pressure rises sharply as the appliance heats up and falls again once it cools
• Water discharging from the pressure relief valve during normal operation
• Pressure gauge reads high with the system cold, or the vessel feels heavy or full of water when disconnected
• Water present at the vessel's air charge valve when the cap is removed
• Frequent topping up of system pressure to maintain normal readings

• Confirm your appliance model against the fit list above, as the vessel is listed for specific Aquaheat Hi and HWI variants
• Check the existing vessel is an 8 litre unit and that the connection and mounting arrangement match
• Inspect the gasket seating face on the appliance before fitting the new vessel
• Isolate the appliance, drain down and depressurise the system before removal