A search for the pair production of heavy vector-like partners $\mathrm {T}$ and $\mathrm {B}$ of the top and bottom quarks has been performed by the CMS experiment at the CERN LHC using proton–proton collisions at $\sqrt{s} = 13,\text {Te}\text {V} $ . The data sample was collected in 2016 and corresponds to an integrated luminosity of 35.9 $,\text {fb}^{-1}$ . Final states studied for $\mathrm {T} \overline{\mathrm {T}} $ production include those where one of the $\mathrm {T}$ quarks decays via $\mathrm {T} \rightarrow \mathrm {t}\mathrm {Z}$ and the other via $\mathrm {T} \rightarrow \mathrm {b}\mathrm {W}$ , $\mathrm {t}\mathrm {Z}$ , or $\mathrm {t}\mathrm {H} $ , where $\mathrm {H}$ is a Higgs boson. For the $\mathrm {B} \overline{\mathrm {B}} $ case, final states include those where one of the $\mathrm {B}$ quarks decays via $\mathrm {B} \rightarrow \mathrm {b}\mathrm {Z}$ and the other $\mathrm {B} \rightarrow \mathrm {t}\mathrm {W}$ , $\mathrm {b}\mathrm {Z}$ , or $\mathrm {b}\mathrm {H} $ . Events with two oppositely charged electrons or muons, consistent with coming from the decay of a $\mathrm {Z}$ 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 $\mathrm {T}$ and $\mathrm {B}$ quarks for a range of branching fractions. Assuming 100% branching fractions for $\mathrm {T} \rightarrow \mathrm {t}\mathrm {Z}$ , and $\mathrm {B} \rightarrow \mathrm {b}\mathrm {Z}$ , $\mathrm {T}$ and $\mathrm {B}$ quark mass values below 1280 and 1130 $,\text {Ge}\text {V}$ , respectively, are excluded.