I bought a tub/shower valve system from lowes. When I turn on the faucet for the tub, the water comes out the tub faucet and the shower head at the same time. Is this a defective valve? Everything seems to be hooked up properly.

Couple of ideas: If you don't get water at all first check to see if the shut-off valves are open. If so, close them and remove and clean the cartridge. If water comes from the spout and not the shower head, make sure the diverter (the handle on the tub spout) moves up when you pull it. If that works, remove and clean the shower head since there might be debris blocking the water flow. Without
more info this is my best guess.

When you turn off faucets other than your tub or shower you will note that the water stops fairly abruptly. Not so with a shower head or tub spout. Some water always dribbles out even after you have turned it off. This small amount of water then evaporates leaving behind the iron that was dissolved in your water. This also happens if any faucet has a slow drip. There are products that will easily remove the rust stains. CLR, Iron Out, or Iron Ike are all good products that will remove the stain. Available at hardware stores, plumbing supply houses, and, ugh, Home Depot or Lowes. Please support your local business owners by purchasing there.

Do you have water coming out of the tub spout and not the shower head? If so how does the water get directed to the shower head,is it by pulling up the diverter on the tub spout?If water is still coming out of the tub spout then the diverter is bad and the tub spout needs to be replaced.

Take the shower head off (and the valve) then turn the shower on and see if water will come out of the shower neck without the head on head on it

To talk about your problem forces me to assume a few things.....If you allow the water to flow without cartridges and handles, the water must be flowing straight through the cartridge channels and out into the tub. It is not flowing through your tub spout or shower head when you test the water this way. If I'm correct, then the problem is isolated to the water mix operation. That means coming out of your spout or shower head. So now I have to ask a question. When you operate as normal (cartridges and handles installed) does your problem show up only on your shower head or does it also show up when operating out of the tub spout? If the problem is isolated to the shower head, try a head replacement. It may be partially plugged. If it's head or spout there may be something in the mixing pipe that only shifts around as pressure increases. I hope that is not your problem. It would require pulling those pipes out for inspection and most likely replacement. Nimsgame

Not unless you had a backward plumber , If the diverter at the faucet is open for tub, then no water will go up the shower, The shower may hold enough water up there to make it look like a drip, Even if the valve was leaking all the time, it would not go up, it would come out the faucet. It only works with pressure. Unless the valve was plumbed wrong,,, Hope this helps.

The faucet may be installed upside-down.

SOUNDS LIKE YOUR ISOLATION VALVE IS AT FAULT .

well the Diverter is not working it dose not matter the distance. when applied it should shoot the water to shower or tub if not working will come both.

Verify the height from the shower valve to the Shower head, the instructions specify the correct distance if it is too short the pressure could be getting up to the shower head.

Perhaps the water pressure it too high at the valve not allowing all the water down the faucet outlet, there are set screws on the sides of the shower valve to adjust the water allowed in the mixing chamber.

Something is restricting the water flow to the faucet, creating enough pressure to send some of the ater supply up to the shower.

I hope some of these ideas help