Expansion vessels

An expansion vessel absorbs the pressure fluctuations that occur as water in a closed heating circuit heats up and expands. It contains a pre-charged air or nitrogen chamber separated from the water side by a flexible diaphragm or bladder, and is typically installed on the return line close to the boiler. Without it, repeated pressure surges would stress seals, valves and the heat exchanger until they fail.

Selecting the correct vessel depends on the total water volume of the system, the working pressure range, the pre-charge pressure, the vessel capacity in litres, and the connection thread size. Always verify the acceptance volume matches your system's expansion factor. Where a direct order number from another manufacturer is known, it can be cross-referenced against our listing to confirm a compatible replacement.