So if the pressure is to high at the faucet creating back pressure and I turn down the water at the main water shut off would that reduce the the pressure enough to stop the water from coming out the shower? I thought so but I was wrong and water still came out the shower head when filling the tub. So here's the question if reducing the pressure there doesn't help then how much help would replacing the pex line for copper be? Unless turning the water down at the main shut off only reduces the flow and not the pressure. Can anyone she'd some light on my situation. I might add that there is a considerable amount of water comin from the shower head and the shower head mixer and faucet are moen products
Sounds like you used PEX to run from the mixer valve to the tub spout. Replace the PEX that goes from the mixer to the spout with copper. You are getting a bypass to the shower because the PEX from the mixer to the spout cannot handle the flow without backing up to the shower head. PEX has a slightly smaller i.d. than copper.