Type I X-ray bursts are thought to be thermonuclear flashes on the surface of accreting neutron stars. We present hydrodynamic multi-zone models for such outburst and the preceding accretion phase. We follow in detail all relevant nuclear reaction rates including adaptive networks with more that 1000 isotopes. Series of subsequent bursts are followed to determine the role of chemical and thermal "inertia" -- the ashes of preceding bursts affect burst re-occurrence time and light curve. But also the inward heat wave of bursts modifies the composition of the ashes of earlier bursts.