At JET the increase of the additional heating power and the ITER-like first wall upgrade planned for 2008 with new Be wall and W divertor will require an improvement of the protection system in order to guarantee the integrity of the first wall. An accurate estimate of the power load and the temperature of the tiles during a discharge will become crucial to prevent damage to the structure. In that perspective the JET protection system (WALLS) has been improved and is in operation at JET. The plasma magnetic information and the input power to the plasma are used to evaluate the thermal load along the first wall. The evolution of the power distribution and tile temperature during and after a discharge are calculated by the system. Termination of the discharge is required if a thermal limit is reached or if a vulnerable area of the vessel is exposed to an excessive level of power. The calibration and validation of the algorithm have been performed comparing the model estimates with the temperature measurements provided by thermocouples and a new Infrared Camera (IR). This paper describes the structure of the WALLS algorithm. The models used to estimate the power distribution and the thermal diffusion are discussed, and the results obtained are compared to the IR camera measurements.