The Worcester Bosch Greenstar 4000 simple switch flue adaptor allows for the use of an existing vertical or horizontal sideways hole through the external wall of the property when replacing an i Junior or Si boiler and it is suitable for use with Greenstar 4000 boilers. A boiler flue is an outlet through which steam and toxic gases resulting from the boiler's normal operation are safely expelled. Different models of flue are chosen to suit the type and location of the appliance.

Brand Name	Worcester Bosch