The answer to 'pipe won't flush' is that there are several common causes, including a clogged drain, a problem with the toilet's flushing mechanism, or a blockage in the main sewer line. Symptoms may include the toilet bowl not draining properly, water backing up, or a slow flushing action.
Some potential solutions you can try yourself include using a plunger to clear a clogged drain, checking the toilet's flushing mechanism for issues, or using a drain snake or auger to clear a blockage. However, if the problem persists or you suspect a more serious issue with the main sewer line, it's best to call a professional plumber to diagnose and fix the problem.