NiTi alloys show mechanical and thermal shape memory which both rely on martensitic transformations which involve the crystallographic phases B2 (high temperature phase), R-phase (intermediate temperature phase) and B19’ (low temperature phase). Martensitic transformations occur in near equiatomic NiTi-alloys with Ni-concentrations ranging from 50 to 51 at.%. Normal heat treatments of Ni-rich NiTi alloys result in the precipitation of lenticular Ni4Ti3-disks on {111}B2 planes. There are four such planes and thus four families of Ni4Ti3 precipitates are normally expected. It is possible to promote the nucleation and growth of only one precipitate variant using <111>-compression aging. This yields a model system which is ideally suited to investigate martensitic transformations in NiTi with precipitates using in situ transmission electron microscopy (TEM). In the present study we use DSC investigations to show that the nature of the martensitic transformations in Ni-rich single crystals changes from two to three steps with increasing aging time. TEM studies reveal that a certain minimum spacing between the precipitates is required for a three step transformation to occur. Mechanisms for three step transformations in single crystals as observed using in situ cooling experiments in the TEM are presented. The results are discussed in the light of recent single crystal results reported in the literature and on the basis of what is generally known about multiple step martensitic transformations in NiTi.