What fails
Water Heater Repair Houston TX: What Usually Fails

Most water heater repair comes down to one part. On gas tanks that is the thermocouple, gas valve, igniter or a dirty burner. On electric tanks it is a heating element or thermostat. On both, relief valves and drain valves wear out.
A plumber tests the part, confirms it failed and quotes before any work starts. If the tank itself is leaking, no part will fix it, and replacement is the honest answer.