Model no on inside of door is pretty essential to know what machine you have Cathy, every bosch machine has Exxcell on the facia, but anyway for the most common type do the following :- unplug machine, remove the screws around the curved backplate on back of machine, (you will need 2 screwdrivers T20 Torx and T15 torx) the large screws go into the metal to metal and the small ones go into the metal to plastic, dont get them mixed up when you refit them. Remove this cover and you will see a thermostat on top of the heater press the little red button on the thermostat till it clicks, refit backplate and it should heat up. This fault usually happens when door filter or condenser box is blocked check them both. Cheers
Kenjo, June 2012