The invention relates to a plate heat exchanger 1 with at least two cuboidal modules 1a, 1b. The two modules 1a and 1b are cuboidal and are each closed to the outside by cover sheets 5. The two modules 1a and 1b are arranged such that in each case, cover sheets 9a and 9b of the same size are directly adjacent. On the contact surfaces, sections 20a, 20b are welded that prevent movement of the two modules 1a, 1b perpendicular to the contact surfaces 9a, 9b either alone or with an additional formed part 50.