Hi there just replace the mixing valve on a hot water tanks all seemed good was bit tough to get off but got it. Replaced it with a new one tightened up and all good no leaks. However when I turned main water from house on then the cold water line into the hot water tank I am now getting a small leak. Tightened it up a bit and tried tightening the middle screw but same. If it is about 3/4 on it has small drip if on about half way more leaks out. My question is how does one fix this does whole shut off valve need to be replaced. Also it is a shut off valve like one on garden house that turns.