A search for the pair production of heavy vector-like partners T and B of the top and bottom quarks has been performed by the CMS experiment at the CERN LHC using proton-proton collisions at s=13Te . The data sample was collected in 2016 and corresponds to an integrated luminosity of 35.9 fb-1 . Final states studied for TT¯ production include those where one of the T quarks decays via T→tZ and the other via T→bW , tZ , or tH , where H is a Higgs boson. For the BB¯ case, final states include those where one of the B quarks decays via B→bZ and the other B→tW , bZ , or bH . Events with two oppositely charged electrons or muons, consistent with coming from the decay of a Z boson, and jets are investigated. The number of observed events is consistent with standard model background estimations. Lower limits at 95% confidence level are placed on the masses of the T and B quarks for a range of branching fractions. Assuming 100% branching fractions for T→tZ , and B→bZ , T and B quark mass values below 1280 and 1130 Ge , respectively, are excluded.