In an extension of the SM with an additional singlet scalar field S and vector-like quarks, we study the condition of the radiative enhancement of a heavy scalar boson decay into a massive gauge boson pair. Focusing on the loop effects, we assume that $S$ is linked to the standard model world only through loops of vector-like quarks. The radiative effects are the mixing with the Higgs boson and the loop-induced decays into $hh$, $WW$, $ZZ$, $gg$, and $\gamma\gamma$. The critical condition for the longitudinal polarization enhancement is the large mass differences among vector-like quarks.