Angle Stop Valve Behind Toilet Coming Apart When Trying to Unscrew The Nut Connected To It

Question

A simple bidet installation got me in a mess. I closed the angle stop valve behind my toilet and removed the flex hose to install 1/2" to 3/8" threaded coupling. Then I connected a 3/8" T-adapter and connected my toilet hose to one end, and a bidet hose to the other. Worked great except for a slow drip between the threads of the stop valve and the coupler, even with 4 layers of Teflon tape. Many re-assemblies later, in an attempt to stop the leak I apparently over-tightened the coupler, and now when I try to loosen it (piece #3 in the picture) piece #2 goes with it, causing water to spurt out between pieces 1 and 2. It happens with the valve fully closed. Turns out the stop valve (a quarter turn valve) is made of 2 pieces threaded into each other, and now I'm disassembling the valve while it's trying to hold back water! I can't just tighten it up again either because the valve/coupler connection still seeps.

Any tricks for binding pieces #1 and #2 together so I can unscrew part #3? Part 2 doesn't have a hex shape to grab with a wrench. Assuming welding them together somehow is not an option since there's water in the pipe.

As for replacing the valve- we're in a condominium which has a cold water shutoff for our unit, but it turns continuously and doesn't shut off the water. I'd probably need to shut off water for all 7 units which requires advanced notice, and confidence. Would like to avoid it if possible.

I'll never over-tighten again and will choose parts with gaskets instead of threads only.

Thanks in advance.

Valve for just my unit. Turns forever, doesn't close.

Valve for whole building. Works fine.

Answer 1

You are correct that trying to repair the stop-valve is a bad idea, and should be replaced.
A reason why your condo shut-off valve is spinning is the thread on the stem has being stripped. That the part that connects the handle to the stem. When you turn the handle, you will see that the stem is not turning.
In my picture, where the Nut is shown, It could be a nut or screw there to attached the handle to the stem. You could try and remove the handle to expose more of the stem. If you can get a clamping plier on the stem, try to and turn slowly clockwise to turn the water off. The stem should be moving in. This would be a temporary fix to cut the water off.
You will still need a plumber to repair this if the threads are stripped.

If you are able to turn off the water to your condo, then it would be a simple matter of replacing the broken toilet stop-valve with a new valve with the proper fitting, 3/8" outlet, that matches your tee.