15 MeV electron irradiated nitrogen doped n-type 4H-SiC has been studied by deep level transient spectroscopy (DLTS). In this study we have investigated the isochronal annealing behavior of two DLTS peaks located at 0.7 eV and 1.6 eV below the conduction band, previously reported in the literature as Z and EH6, respectively. We have detected two new centers, contributing to the Z and EH6 peaks, labelled as Z* and EH6* and located at 0.66 eV and 1.59 eV below the conduction band, respectively. After heat treatments between 500 degreesC and 1100 degreesC the amplitudes of Z* and EH6* show a close one-to-one correlation. It is suggested that these two levels represent two different charge states of the same defect. Further, no Poole-Frenkel effect is observed, indicating a center of acceptor type.