Wafers of float zone Si grown in hydrogen (Si[H]) were annealed at various temperatures in the range of 300–750 °C before irradiation with 5 MeV electrons. It was found that hydrogen‐related deep levels were no longer observed, when the preannealing temperature was above 500 °C (450 °C) in the case of irradiatedn‐type Si[H] (p‐type Si[H]) samples. Similarly, the convergence of annealing temperatures of different irradiation defects towards a common temperature normally observed in Si[H] was no longer observed, if the Si[H] sample had been annealed at or above 550 °C. A dynamic model is proposed to explain the experimental results.