Expansion Vessels

About our Expansion Vessels

Reflex vessels from Altecnic offer the highest quality German engineering with market-leading British service and the UK's most comprehensive 5-year warranty.

Expansion Vessels FAQs

What is an expansion vessel?

Expansion vessels sometimes referred to as expansion tanks, are used within most domestic heating systems. The purpose of an expansion vessel is to maintain the correct pressure within the system, which ensures your boiler functions effectively.

Expansion vessels consist of a cylinder avoided by a rubber membrane (or diaphragm) (separating the water in the central heating system from the pre-filled nitrogen chamber.) They will also feature a valve which allows for repressurising and depressurising as necessary.

How does an expansion vessel work?

When heated, water within a central heating system will expand. If this extra volume of water has nowhere to go, the pressure within the system increases to a system-critical level. At this point, the safety relief valve lifts to discharge pressure. By using an expansion vessel, the expanded water has somewhere to be displaced. As a result, the water fills the bottom of the tank, compressing the nitrogen above and regulating the pressure within the system.

Where should an expansion vessel be located?

Expansion vessels are usually located within the casing of the boiler. If required, external expansion vessels should preferably be fitted on the return pipe work to the boiler.

Please note, by law boiler casings must only be removed by Gas Safe registered engineers.

What happens if an expansion vessel fails?

If an expansion vessel fails, the pressure within the system will fluctuate and could cause system failure, resulting in loss of hot water and central heating.