The free convection boundary layer on an insulated wall formed by local internal heating through a modified form of Arrhenius kinetics is considered. It is shown to involve two dimensionless parameters, the activation energy and the rate of local heating. Numerical solutions to the initial-value problem are obtained showing that, for relatively weak internal heating (small ), a nontrivial flow arises at large times, whereas for larger local heating the solution becomes singular at a finite time. This behaviour is also seen to depend on the size of the initial input. The corresponding steady states, being the possible large time solutions to the initial-value problem, are also treated. These show the existence of a critical value of , dependent on . These critical values determined numerically showing that there was a finite region of the parameter plane over which steady states cannot be found. Asymptotic forms for both and being small and large are derived.