I have had this problem twice on my machine now. I had to completely remove the detergent drawer and then seperate the top/bottom halves and then remove another piece of plastic inside the top part to expose the water channel for the conditioner. Mine had become completely blocked with black gunk, lord only knows how. It was causing the conditioner holder to almost fill up with water but not enough to start it syphoning out into the drum.
Paul Bignell, November 2008