The Resideo AT140A1000 Transformer is a reliable 120V to 27V step-down transformer designed to provide stable low-voltage power for HVAC controls. Delivering 40VA, it supports thermostats, zone valves, relays, and furnace or boiler control circuits. The transformer works by converting line voltage to a safe control voltage, ensuring consistent system operation. https://www.partshnc.com/at140a1000-resideo-40va-tranfmr-120v-27v-sec