The stability of the weld surface quality resulting from laser–arc hybrid welding of 4 mm thick steel was studied. The trends of stability in terms of top weld width variation were estimated by using design of experiments, where different types of unstable welds were distinguished. High speed imaging of the process supported the interpretation of the trends. High arc voltage and short distance laser–arc has destabilized the process. For a stable process the applied spray mode has caused a short arc and symmetric central drop transfer while for high voltage the arc became long and wide and the drops traveled sideward. The potential and limits of the design of experiments method for such kinds of applications were discussed.