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🔵🔴⚪ What Do Expansion Vessel Colours Mean? - BER Assessment

  • Mihai
  • 3 days ago
  • 1 min read


BER Assessment - easy identification of a domestic hot water expansion vessel
Domestic Hot Water Expansion Vessel

🔴 Red Expansion Vessel

Used for:

  • Domestic hot water (DHW)

  • Unvented hot water cylinders

Why red?

  • Designed for potable water

  • Internal diaphragm and lining are suitable for drinking water

  • Rated for higher temperatures

➡️ This is the most common vessel used with unvented cylinders


🔵 Blue Expansion Vessel

Used for:

  • Cold water systems

  • Boosted cold water

  • Sometimes heating (manufacturer-dependent)

Important:

  • Generally not suitable for hot potable water

  • Lower temperature rating

  • Different diaphragm material

➡️ Not normally acceptable for unvented hot water expansion


⚪ White / Grey Expansion Vessel

Used for:

  • Sealed heating systems (radiators, boilers, heat pumps)

  • Closed-loop systems (non-potable)

Important:

  • Not for drinking water

  • Internal materials are not approved for potable use

➡️ Must NOT be used on domestic hot water systems


✅ Simple Rule of Thumb

  • Hot potable water (unvented cylinder) → 🔴 Red

  • Cold water only → 🔵 Blue

  • Heating systems → ⚪ White / Grey


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