Why won't my hot water heater stay lit, and what could be causing this issue?

A common reason why a hot water heater won't stay lit is a faulty thermocouple, which is a safety device that detects if the pilot light is on. If the thermocouple is malfunctioning, it may shut off the gas supply to the pilot light, causing it to go out. Other possible causes could include a dirty pilot light, a clogged gas line, or a problem with the gas valve. It is recommended to have a professional inspect and repair the hot water heater to determine the exact cause of the issue.