The "EF" prefix signifies that the valve is equipped with an explosion-proof and watertight enclosure

turn it counterclockwise

required for a professional field installation in accordance with Viessmann service standards

With port configurations of 3/4" x 1/2"

This specific gauge is designed for Weil-McLain EG

Resideo AT72D1089 Transformer 323269-701 The "EF" prefix signifies thatThe Resideo AT72D1089 Transformer is a professional grade solution for technicians requiring a reliable 120V to 24V step down for HVAC control circuits. Engineered with a 40VA power rating, this unit is built to manage the electrical load of 24VAC thermostats, gas valves, and multi zone relays. The hardware features a 4"x4" plate mount design and a NEMA Type D enclosure, ensuring compliance with NEC Class 2 (not wet) and Class 3 (wet) requirements.