OK, the story gets more odd. Just to make sure I have the terms right, I call the black insert with the spinning pump the “cartridge”, and the yellow pump housing the “housing”. I just went out and switched the cartridges, putting the recirc cartidge in the aerator housing and vice versa. Both work fine! Then I switch them back to the original way, and the aerator pump again slows down and stops. Put it in the recirc housing, runs fine. Have to admit, I am a bit stumped. Oh, it is a 2003 Pantera IV. I bought it in June of 2006. It worked perfectly until this past Sunday.