Transient transport and heat modulation experiments are routinely carried out at most of the major devices and have proved powerful tools for testing various physics-based transport models. Experiments in JET have shown that the transient propagation of a cold pulse initiated by a local cooling near the plasma edge is found to be much faster than the propagation of the heat modulation. This poses a serious challenge to modelling and up till now it has apparently not been possible to explain both effects within the same model. The modulation experiments are well described by the critical gradient model, CGM, which, however, cannot describe fast propagation of the cold pulse for the same parameters.