Dishwasher problems

Have an ongoing problem with my Carlton CS2S dishwasher, dishwasher is about 18 months old, firstly had a problem with the timer sticking halfway through the wash cycle & the water not heating up, heating element was ok, turned out to be a faulty protection thermostat, changed this & dishwasher worked fine for a couple of weeks. Then, switch timer on, unit will fill with water, then clicks on to wash position & then seem to be getting a buzzing sound coming from the drain pump, but not all the time, other times it starts the wash cycle & seems ok but then it wont heat up the water again, I think protection thermostat may have gone again. Now, the motor is running continuously whatever position the timer is switched on to. Any suggestions?