This paper considers the results of an experimental study of non-stationary nucleate boiling that develops on the heater surface as a result of abruptly escalating heat inputs. The isolated bubble model that is commonly used to describe nucleate boiling on a surface has a number of limitations. First, we have to describe the characteristics of an ensemble of bubbles instead of an idealized object, which is a single vapor bubble. Second, three different ways of interaction between bubbles (hydrodynamic, thermal, and mass transfer) are possible on the heat-releasing surface, the contribution of which should be taken into account. In the present study, we highlight the influence of these important factors on the determination of heat transfer during the development of unsteady boiling. Two regimes of nucleate boiling that are significant for numerical simulation were identified. The first one is described by existing models and represents the existence of isolated bubbles. The second regime begins with an active mass transfer between closely spaced bubbles that give rise to specific structures - bubble clusters. Such key characteristics of nucleate boiling as separation diameter, nucleation frequency, and density of vaporization centers require a special approach due to clusters that occur on the surface. The analysis of the results of high-speed video shooting (200,000 frame/sec) revealed that we have to refine the initial data of the existing heat flux partition wall boiling models. The existing approaches to determining heat transfer under nucleate boiling conditions can be extended from isolated bubbles to the formation of stable vapor structures above a heat-releasing surface.