The Navien 30015811B Air Pressure Sensor is a replacement monitoring component designed for use in compatible Navien tankless water heaters and combi boiler systems. It works by measuring air pressure within the combustion and venting system and transmitting data to the control board to ensure proper airflow conditions. This helps maintain safe and efficient operation by verifying tha... https://www.partshnc.com/30015811b-navien-tankless-water-heaters-air-pressure-sensor-aps-02-a