The epsilon-mechanism is a self-excitation mechanism of pulsations which acts on the regions where nuclear burning takes place. It has been shown that epsilon-mechanisms can excite pulsations in models of hot helium-core flash, and that the pulsations of LS IV-14o116, a He-enriched hot subdwarf star, could be explained that way. We aim to study the epsilon-mechanism effects on models of hot pre-horizontal branch stars and determine, if possible, a domain of instability in the log(g) - Teff plane. We compute non-adiabatic non-radial pulsations on such stellar models, adopting different values of initial chemical abundances and mass of the hydrogen envelope at the time of the main helium flash. We find a new theoretical instability domain of long-period (400 s < P < 2500 s), g-modes for models with 22000 K < Teff < 50000 K, and 4.67 < log(g) < 6.15.