The Lochinvar & A.O. Smith 100112658 0.27" Pressure Switch Kit is a safety control component designed for compatible gas-fired boilers and water heater HVAC systems. It monitors air pressure within the venting system and confirms proper airflow before allowing the burner to operate. If the required pressure is not detected, the switch interrupts the ignition sequence to help prevent u... https://www.partshnc.com/pressure-switch-027-for-lochinvar-a-o-smith-part-100112658