Fitted mine last week. It didn't work at first even though it was all wired up correctly etc.
After a couple of emails back and forth with Dr Bean, we figured out that the problem was caused by the studs and the holes in the circuit board not lining up correctly.
I could just get the retaining screws in, but it must have caused some pressure on the circuit board which caused problems with the optical sensor.
To fix it, I simply swapped the studs (left to right hole, right to left hole) and the circuit board holes lined up correctly. Once I had it reassembled, the pump worked OK.
So the moral is to make sure the screws fit easily into the circuit board with no side pressure.
Here's a pic of how it was before I swapped the studs - CP, feel free to include it in your instructions to show what not to do...