The answer to 'pipe repair won't flush' is that a clogged or partially blocked pipe is the most common cause. This can happen after a repair if the pipe was not properly cleared or if there is a deeper blockage in the system. Symptoms include slow or no water drainage and a gurgling sound in the pipe.
To troubleshoot, first try using a plunger or plumber's snake to clear the blockage. If that doesn't work, you may need to disassemble the pipe to inspect and clean it out. If the problem persists or you're uncomfortable working on the pipes, it's best to call a professional plumber to diagnose and fix the issue.