An instant hot water dispenser has an upper plastic tank section connected to a lower brass tank section by a safety clamping arrangement which includes outturned tabs on the upper plastic tank section which interfit in notches in the brass lower tank section and a retainer ring located between the plastic tabs and outturned metal flanges on the brass tank section. An O-ring seal between the plastic upper tank and the brass tank provides a fluid seal. Various of the plumbing connections are integrally molded with the plastic top and expansion chamber cover which is separated from the main water tank by a common wall or partition. An aspirator opening in an integrally formed plastic stem in the expansion chamber cover aspirates water from the expansion chamber as incoming cold water passes the aspirator opening.