Ok if you know the heater is fine then this just leaves either the wiring to the heater or the control board itself. As the control board has a heater relay which can fail on these Bosch appliances just like any other brands to be honest.
So may be worth just checking the wiring block to the heater and then remove the outer door panel and check the wiring harness for any trap or broken wires.
But if that's fine and its filling up ok with water then it all points to the control board. You can check that first for any dry joints or burn marks which you can resolder and saves the cost of a new part. But if it looks ok then its probberly the board itself that's the fault here.