I will present a generic search for a heavy scalar boson using 13 TeV proton-proton collision data acquired by the CMS experiment in 2015. Events in the decay channel H->ZZ->2l2v are selected from data corresponding to an integrated luminosity of 2.3 fb^-1. An analysis of the reconstructed transverse mass and missing transverse energy is performed in different event categories, and limits are set on the production cross section of a heavy scalar of variable width in the gluon-fusion and vector-boson fusion production modes. The limits are interpreted as constraints on the production of a heavy scalar in the electroweak singlet model. They are stronger than the Run 1 analysis results in the mass range around 1 TeV and above. Constraints are also set in the tan beta - mH parameter space of specific Type-I and Type-II two-Higgs doublet models.