Symbiotic stars are the widest interacting binaries with orbital periods of a few years consisting of a red giant as the donor and a white dwarf as the accretor. According to behaviour of their long-term optical light curves we distinguish between the so-called quiescent and active phases. In most cases, the latter are characterized by a few magnitudes (multiple) brightening(s) with signatures of a mass-outflow on the timescale of a few months to years. They are called `Z And-type' outbursts as have been observed from the past for Z Andromedae - a prototype of the class of symbiotic stars. On a sample of classical symbiotic stars (Z And, AX Per, BF Cyg, CH Cyg, AG Peg and AG Dra), using the method of multiwavelength modelling the SED, I will introduce basic characteristics of Z And-type outbursts and discuss their possible origin.