My pump system clogged with my first attempt with the Grainfather at the most inopportune time - when initializing the counter-flow cooling process. I was able to fix the issue by turning the pump off and disassembling ball valve, near the top of the tube from the pump. Inside the ball valve is a spring where hops had log-jammed and formed a tight plug. I poked the hop plug out of the spring and reassembled the ball valve and was back in business; all in about 3 mins. I've heard that others have just removed the ball valve guts all together as a quick remedy. The clog was a first-timer issue. It's not happened since.