Experimental investigations of the nucleate pool boiling on thin heaters have been conducted by simultaneous observations of the boiling surface and by measurements of the transient temperature field on the heater. The local heat flux and the heat transfer coefficient distributions have been calculated at various boiling intensities. Fast and slow bubble growth mechanisms have been identified. Significant increase of the local heat flux has been calculated below the fast growing bubble at the nucleation phase. An important increase of local heat flux within the triple wall – liquid – vapor contact line of the slowly growing bubbles has been shown. The phenomenon of the chain coalescence has been presented together with its importance for cooling of the heated surface. During boiling at high heat flux, locally superheated spots on the heater surface expand and merge into large superheated areas. This can lead to the critical heat flux.