They're supposed to have a deep clean once a month with the filter removed and cleaned out. It could be that some murky stuff has got caught up in its base and the hot weather is causing it to rot. Also, in this hot weather, if you don't have it sufficiently filled to run every day, at least put it on the cold pre-wash cycle to remove the worst of the residue.
Clean your filters out - get Finish dishwasher cleraner and follow instructions then get some Mr.Muscle kitchen cleaner and give the door and seals a good cleaning to get rid of all the gunge that collects around them - this will get rid of nasty niff.