After inspecting the water heater, I found that the limit switch had tripped, which was preventing the unit from operating. I reset the switch and relit the water heater, ensuring it was running properly again. However, during the inspection, I also noted that the system lacks a chimney liner, which is necessary for proper venting. A chimney liner will need to be installed to ensure safe operation and prevent potential venting issues in the future. The water heater is now functioning, but further work is required.