According to Cerda et al. (Computers chem. Engng 14, 197, 1990), a heat exchanger network is structurally flexible for a given variation range of parameters if it guarantees operability (feasibility) and maximum energy recover in the whole set of operation points. In this paper we present a flexibility test (in the previous sense) at the level of heat matches when only heat capacity flowrate variations are allowed. This test is a mixed integer linear program which considers the whole set of operation points at once, and may be incorporated into any synthesis procedure of flexible heat exchanger networks [like the one proposed by Floudas and Grossmann (Computers chem. Engng 11, 319, 1987)] that combines synthesis techniques and flexibility analysis.