The Worcester Bosch 4000 Simple Switch Flue Adaptor in white is a unit designed for use with storage tank water heaters, specifically the Greenstar 4000 boiler range. It features a flue adaptor for easy installation and is sold as a single unit. This product is perfect for those looking to connect their heating system to a specific boiler model while maintaining a sleek and efficient design. The white colour adds a touch of elegance to the overall setup, making it a practical and stylish addition to any home heating system.