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Heating vs Potable Expansion Vessels

Expansion vessels are used to absorb pressure changes in sealed plumbing and heating systems, but choosing the correct type is extremely important. Heating expansion vessels and potable expansion vessels are designed for different applications and should never be mixed incorrectly.

At Edwins Plumbing & Heating Supplies in West London, we stock a range of expansion vessels for both heating and potable water systems, including sizes suitable for domestic and commercial installations.

What Is A Heating Expansion Vessel?

Heating expansion vessels are used within sealed central heating systems. As water heats up and expands, the vessel absorbs the increase in pressure to help protect the boiler, pipework, valves, and other heating components.
Heating vessels are commonly used with:

  • sealed heating systems

  • combi boilers

  • system boilers

  • radiator circuits

  • underfloor heating systems

Most heating expansion vessels are red in colour.

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What Is A Potable Expansion Vessel?
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Potable expansion vessels are designed for drinking water systems, particularly unvented hot water cylinders. These vessels are manufactured using materials suitable for potable water applications and are typically WRAS approved.
Potable expansion vessels are commonly installed with:

  • unvented cylinders

  • mains pressure hot water systems

  • potable water pipework

  • hot water storage systems

Potable vessels are commonly white, blue, or stainless steel depending on the manufacturer and system type.

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Why The Difference Matters


Using the wrong expansion vessel can lead to:

  • water contamination risks

  • pressure problems

  • reduced system lifespan

  • manufacturer warranty issues

  • non-compliance with regulations

Potable systems require vessels designed specifically for drinking water use, while heating vessels are intended for closed heating circuits only.

Common Signs Of Expansion Vessel Problems

Common symptoms of a faulty or incorrectly sized vessel include:

  • pressure relief valve dripping

  • heating pressure rising excessively

  • boiler pressure dropping repeatedly

  • noisy pipework

  • water discharge from safety valves

  • unstable system pressure

Expansion Vessels Available From Stock

At Edwins Plumbing & Heating Supplies, we stock a range of heating and potable expansion vessels suitable for various domestic plumbing and heating systems.
Typical vessel sizes include:

  • 2 litre

  • 5 litre

  • 8 litre

  • 12 litre

  • 18 litre

  • 24 litre

  • 35 litre

Collection available from our West London trade counter.

Need Help Choosing The Correct Expansion Vessel?

If you are unsure whether you require a heating or potable expansion vessel, our team can help identify the correct option for your system.
We supply plumbing and heating products for both trade professionals and public customers across West London.

Expansion vessels in stock in West London

At Edwins Plumbing & Supplies we stock a wide range products for your heating & hot water system including radiator valves, boiler spares, thermostats and zone valves and many more.

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