It has been observed that for endothermic decomposition processes a thermal analysis unit may fail to follow the programmed temperature. A more thorough study shows that the magnitude of the failure of a thermal analysis unit, i.e. the difference between the experimental and programmed temperature, is dependent on the type of the instrument and is also influenced by the heating rate, the mass of the sample, the enthalpy change (Delta H) of the process, the purge gas and the flow rate.