A method of heat treating a localised region of a component including providing a heat treatment assembly with two or more subassemblies. Each subassembly is configured to partially circumscribe a portion of the component for heat treatment. Each subassembly includes a housing configured to partially circumscribe a portion of the component. An insulator and a heater are provided within the housing and extend to partially circumscribe a component and are arranged such that the insulator is between a wall of the housing and the heater. The method includes positioning the subassemblies adjacently around the component so that the subassemblies fully circumscribe the component. The subassemblies are connected together. The method includes activating the heater to heat the component in a region adjacent the heater.