Make sure the heater is placed UNDER the meal before activating with water. If the heater is on top of the meal, the water will not make contact with the heater and therefore no heat will be generated. Equally, if during meal insertion, the heater has been bunched up at the bottom of the sleeve, it will not work as efficiently. MAKE SURE THE HEATER STAYS FLAT UNDER THE WHOLE MEAL. It is also possible that the heater and meal inside the sleeve were not kept reasonably flat initially (first 30 seconds). The heater needs to absorb the water through each membrane and heater element to obtain maximum efficiency.