We had this a fortnight ago with our old trusty Bosch.
We started with running it on hot, empty to see if that helped. We got a hot dishwasher with the powder spread out down the door. 
We only have a tabletop dishwasher but it's the mainstay of sanity in the house (there's only so much cleaning a F/T WOHM and WOHD can do!) We then tried a Finish cleaning thing but it came out of the wash as full as it was when we put it in. So hot water wasn't getting sprayed.
In the end I took to sneaking peeks quickly when it had been on a few minutes. No water droplets on top (apart from those which could have been condensation). Then I placed the rotor in one position and put it back on again. Turned out that the rotor arm wasn't going round or spraying. So though there was hot water in the bottom, none of it was going on the pots.
I did the maths (callout fee, several days' wait, exorbitant fee for a 10+ year old dishwasher which may not have had parts available) and came to the conclusion that it was time for a new one.
Then nearly posted my first AIBU as it was darned near impossible to get a new one inside 24 hours! (Internet shopping is actually slowing things down a lot, but it's got to the stage when even main stores don't have stock any more and just tell you to go to their websites)
John Lewis
had a four day lead time! None in stores! I nearly melted down at that point.
But my story has a happy (if costly) ending. I took delivery of a new one about 18 hours after the old one officially died. From Boots of all places! (Who knew they had an online, deliver-24/7 white goods dept?) Seriously steep delivery charge but offset by Advantage points, which were almost the same amount.
And the new one is about 50% bigger in usable volume so it's taking some filling!