Can you post the E-Nr number from the appliance please?
It's normally etched across the top of the door.
OK, thanks for that.
If you set the arms at a front to rear position, allow the dishwasher to start washing and quickly open the door, is there water jetting out of the top spray arm?
Does your machine have a 1/2 load button?
I'm sorry if I'm repeating things you've already done.
Check the top spray arm, especially the end holes as these propel the arm.
Also check along the seam, if they are split they tend to leak there instead of spinning.
Hope this helps.
If the spray arms are good and clear, the feed tube is clear then we are looking at something within the heater box or the circulation pump.
Either the pump isn't pumping properly and there's a lack of water pressure or there's an obstruction in the heater box.
The parts exploded view doesn't state that the heater has an alternating valve so I've discounted that as a possibility.
Sorry, you've done all the normal checks and everything seems sound.
I'll opt out of the question and open it to all experts again. Hopefully one of them may come up with something I've missed.
Good luck with it.