Responded to a service call for a wall-mounted gas heater that was not operating correctly. Performed a full diagnostic inspection, including checking gas supply, pilot/ignition system, thermocouple, gas valve operation, and safety controls. Inspected venting and airflow to ensure proper combustion and safe operation. Identified the cause of the malfunction and completed necessary adjustments and repairs to restore reliable heat. Verified unit operation and ensured heater was running safely and efficiently before leaving the job site.