I recently saved a new customer a bunch of money. He called to tell me that his old water heater had given up the ghost and he probably just needed a new one. I drove out and took a look, but I couldn't find anything actually wrong with the equipment except it needed a good cleaning.
A gas water heater requires unrestricted airflow, a clean pilot line, and a clean burner area in order to efficiently heat the water. There are safeties in place to turn off the burner if it cannot burn the gasClick here to read more.