most of my blockages have come due to salt and uratic acid build up in the hoses and joker valve(s). I just ordered 2 Joker valves from Phil to replace
the originals. They have been forced to take a set and will not completely close properly. The salt build up sets you up for a stopped up head and what would normally pass without issue gets stuck on the salt buildup. As long as you have it apart you might want to check out the fittings in front and behind the Joler Valve for build up. If you have any I would invest the extra tlme and clean or replace the hoses. In any event, I would certainly clean the build up off the internal head parts. Good luck.