A couple months ago I had the water heater repalced. I hardly ever use the master tub, but last week turned it on and found a blue/green powdery substance coming out of the fauet. Several table spoons full each time you run the tub. Whatever it is, is is now in my shower line and blocked it and there is hot water pressure. I had the plumber who installed the water heater come back out and they don't know what it is, said to keep running the tub and hope it clears. It's not working! Any ideas?
I'm guessing a flux build-up or residue, but that may be just adding to the problem. Anytime you shut-off water and do plumbing repairs, when the water pressure is restored, the lines have to be flushed out of sediment and debris. Something like a piece of dirt may have lodged inside the body of the shower valve or diverter. If it worked fine before, call that plumber back AGAIN and have him make it right.