The answer to 'shower constantly running' is that a constantly running shower is typically caused by a faulty shower valve or a problem with the shower cartridge. The most common symptoms are a shower that won't shut off completely or a shower that drips constantly, even when turned off. This is a common plumbing issue that often requires the expertise of a professional plumber to diagnose and repair.
If the shower is constantly running, the first step is to try tightening the shower handle or adjusting the trim. If that doesn't work, the issue is likely with the internal shower valve or cartridge, which will need to be replaced. This is usually a job for a professional plumber, as it requires disassembling the shower and potentially cutting into the wall to access the plumbing.