The Worcester Bosch washer and mounting set is a popular spare part for common boilers such as the Greenstar 24i, Junior 24i, 28cdi, 30si, 35CDi, and 42CDi. This set includes various washers, O-rings, and gaskets used in different sections of the central heating system. These components are made from different materials and are designed to seal pipework to other boiler parts, including heat exchangers and gas valves. When installed correctly, they are crucial for preventing gas and water leaks. Boiler spare parts must be fitted by a certified Gas Safe engineer.