lWe study the impact of an undesired simultaneous or consecutive exothermic reaction on the behavioral feature of a boiling slurry reactor (BSR). The BSR is fed by a solution of a non-volatile liquid reactant and a gaseous reactant, while the effluent consists only of gas. While, the BSR can have only a unique steady state if a single reaction occurs, the undesired reaction may lead to the existence of multiple steady states. A unique feature of the BSR is the possible existence of fill-up and dry-up states at which the reactor volume changes monotonically while the other state variables remain unchanged. The fill-up state will lead to spillover unless the feed conditions are properly adjusted. An undesired consecutive reaction leads to more intricate dynamic features than does a simultaneous undesired reaction.