A housingless plate heat exchanger including a plate stack defining fluid passages, at least one collecting tank with a peripheral edge enclosing one end of the plate stack, and a valve receivable in the collecting tank through an assembly opening of the soldered collecting tank and plate stack. The collecting tank and plate stack are soldered together and have a fluid opening. A method of manufacturing the heat exchanger includes the steps of assembling plates of the plate heat exchanger in a plate stack, placing a collecting tank on one end of the plate stack, soldering the plate stack and collecting tank together, and after the soldering step mounting a valve in the collecting tank.