Shower valve question

So I gutted my bathroom and am installing a new shower. I bought a single lever Delta valve and the corresponding rough-in housing for it.
After piping everything up, this is what happens.
If I open the cold water valve, there are no leaks and no water flows, but when I turn the lever 'on', nothing happens.
If I then open the hot water valve, water just starts flowing from the tub spout...even with the lever in the 'off' position. Moving the lever does nothing and water just continues to flow from the tub spout until I shut off the valve.
What I find really interesting is that if I open the hot water valve first, there are no leaks and no water flows, but if I then open up the cold water valve, water flows from the tub spout and the lever does nothing.
So the bottom line is, when BOTH hot & cold water valves are opened up, water flows from the tub spout and the lever does nothing. I can't shut the water off.
Any ideas? Did I buy the wrong type of valve?

With the limited information, and no picture to see what you got, I'd first try to rotate the cartridge, if at all possible. Also, make sure the arrow is pointed up on the valve to make sure you didn't install the valve body upside down.

havasu said:

With the limited information, and no picture to see what you got, I'd first try to rotate the cartridge, if at all possible. Also, make sure the arrow is pointed up on the valve to make sure you didn't install the valve body upside down.

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Havasu - thanks so much for the reply. I will post a picture after I get home from work, but I triple checked to make sure I didn’t install the valve body upside down. (It is well marked all over the place, so I know that’s not the issue.) I also tried flipping the cartridge body, just in case that was the issue, but it didn’t make any difference.
It’s like the valve is doing absolutely nothing. The water just runs up through the supply pipes, through the valve body, and down the tub spout. (But it only happens when BOTH hot and cold supply lines are opened.)

Take a picture and did you leave the cartridge inside while hiking up the new valve? I’ve seen sometimes solder gets inside the cartridge if you don’t flush it before installing it back in.

Rossando said:

Take a picture and did you leave the cartridge inside while hiking up the new valve? I’ve seen sometimes solder gets inside the cartridge if you don’t flush it before installing it back in.

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Rossando - Thanks for the response! I took a few pics which I'll post here. I think I did have the cartridge in when I first turned on the supply valve, so I suppose it's possible that a tiny bit of solder got into the cartridge, but I don't know that that would explain why water flows out of the tub spout even with the shower valve lever in the 'off' position.

havasu said:

With the limited information, and no picture to see what you got, I'd first try to rotate the cartridge, if at all possible. Also, make sure the arrow is pointed up on the valve to make sure you didn't install the valve body upside down.

Click to expand...

Havasu - Here are a few pics....not sure if they will help at all. If you notice anything in the cartridge or rough in housing that might cause water to flow through the tub spout even while the shower lever valve is turned off, let me know. Thanks!

I'm wondering if by chance that is the wrong cartridge? For a quick answer, call the manufacturer and they can probably spell out the problem quickly.

havasu said:

I'm wondering if by chance that is the wrong cartridge? For a quick answer, call the manufacturer and they can probably spell out the problem quickly.

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The problem has been solved! It was just a defective cartridge. It was the right model, it just happened to be defective. I replaced the cartridge and everything is perfect. thanks for the help!!

Rossando said:

Take a picture and did you leave the cartridge inside while hiking up the new valve? I’ve seen sometimes solder gets inside the cartridge if you don’t flush it before installing it back in.

Click to expand...

Hey, the problem is solved! It was just a defective cartridge. Thanks for the help!

Great news. Thanks for letting us know.