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I had a customer last yr with 3 zones via pumps and was getting ghost flow in another zone making very hot. he had no flow check so i installed 3 cast iron flow checks.. It fixed problem for rest of season. now he is having problem again.. I cant believe the flo check valve went bad.. Any advice what to look for? I can install zone valve on that zone which would be a sure fix ( or replace that flo check on that zone) but he is upset.. I would be too if i were the customer.