This Worcester Bosch control knob is a genuine replacement part designed for specific Worcester Bosch boiler models. It is installed on the front control panel and allows for manual adjustment of various boiler functions, such as temperature control or independent operation of hot water and central heating. This ensures flexible and convenient use of your boiler system. Worcester Part Number: 87161410440. Compatible with Worcester 24 & 28 CDI Boilers, Worcester 26 CDI Xtra Boilers, and Worcester 35 CDI (Mark 2) Boilers.