The present invention relates to an impeller assembly wherein a coupling method between an impeller and magnet is improved, more specifically to an impeller assembly which prevents cracking in the inner circumference of the magnet from external forces by applying a guide screw coupled with the end of the impeller and the inner circumference of the magnet and facilitates assembly and disassembly. Furthermore, the impeller can be used for chemicals, medicines, foodstuffs, etc., because metal components are not used therein. In addition, the present invention relates to a hot water boiler using the impeller assembly. According to the present invention, the impeller assembly with improved assembly efficiency comprises: an impeller with a blade unit and a coupling unit, the guide comprising a corresponding coupling unit coupled with the coupling unit of the impeller, and the magnets which are arranged on the outer circumference of the guide.