Hi Sue model no would be good so i can visualise your exact machine... in general on bosch machines if you unplug the machine, then remove the back panel of the machine you will see the heater assembly, on top of this you will see a small thermostat with a little red button on it, push this button till it clicks, refit back and see if it gets hot, clean filter in door and condenser, bottom of machine. If this doesn't make sense post your model no found on the inside of the door. Cheers
Kenjo, January 2015