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Weil McLain 381-800-474 Vent Damper

Weil McLain 381-800-474 Vent Damper

Weil McLain

The Weil McLain 381-800-474 Vent Damper Assembly is the factory 4-inch automatic vent damper for the Weil-McLain CG-25-3, CGa-25, CGa-3 and CGx-3 gas-fired cast iron boilers. Weil-McLain's own CGa Series 1 and 2 replacement parts list shows the 4-inch vent damper assembly as 381-800-474 for the CGa-25 and CGa-3 and cross-references it to the Field Controls GVD-4 and the Effikal RVGP-KS-4BKF damper models. An automatic vent damper is a motor-driven damper blade that sits in the flue connection. It closes the vent while the boiler is idle so that heated room air is not drawn up the chimney between cycles, and it opens fully on a call for heat before the burners are allowed to light. On a system of this type that open-before-fire interlock makes the damper a combustion safety device, not just an efficiency accessory.

Vent dampers are diameter-specific, and the 381-800-474 is the smallest of the Weil-McLain gas boiler damper family. The CGa Series 1 and 2 parts list pairs each boiler size with its own damper: the 381-800-474 (4-inch) for the CGa-25 and CGa-3, the 381-800-475 (5-inch) for the CGa-4, the 381-800-476 (6-inch) for the CGa-5 and CGa-6, and the 381-800-477 (7-inch) for the CGa-7 and CGa-8. The same parts list shows the vent damper harness 591-391-795 and the vent damper actuator 510-512-337 as separate service parts, which matters when the damper body is sound and only the harness or actuator has failed. The 381-800-474 is the complete assembly: as pictured, a stainless-steel damper body stamped with a rotation marking, the motor and actuator housing mounted on top with a short flexible metal conduit, a multi-color wire lead ending in a plug-in connector, and two small loose mounting pieces packed alongside.

A failed vent damper usually shows up in one of three ways: the boiler will not fire because the damper never proves open, the damper sticks closed or only partly open and the boiler locks out or spills flue gas, or the damper sticks open and the boiler loses efficiency between cycles. Before condemning the assembly, shut off power and gas, confirm the blade turns freely by hand, check that the harness plug is fully seated and the wires are not chafed or heat-damaged, and verify the boiler control is sending the damper its signal on a call for heat. If the blade is seized, the actuator is dead or the body is warped, replace the complete 381-800-474 assembly. Install it with the rotation marking oriented as Weil-McLain's instructions show, secure it to the flue connection per the boiler manual, connect the harness, and run a full cycle to confirm the damper opens before ignition and closes after the burner shuts down. Never bypass or wire around a vent damper: an inoperative damper on a gas boiler is a carbon monoxide hazard.

Key Benefits

  • Factory Weil-McLain Fit: The 4-inch assembly specified for the CG-25-3, CGa-25, CGa-3 and CGx-3 boilers, not a universal damper.
  • Complete Assembly: Damper body, actuator housing, flexible conduit and wire lead with plug in one part, so there is no piecing together a damper from separate components.
  • Restores the Safety Interlock: A working automatic vent damper proves the vent is open before ignition and closes it when the boiler cycles off.
  • Easy Cross-Reference: The parts list ties this assembly to the Field Controls GVD-4 and Effikal RVGP-KS-4BKF, so you can match it to the damper on the boiler now.

Common Questions

  • Which boilers does the 381-800-474 fit? It is the 4-inch vent damper for the CG-25-3, CGa-25, CGa-3 and CGx-3 boilers. Confirm against the boiler's model and serial number before ordering.
  • Can I use the 381-800-475, 381-800-476 or 381-800-477 instead? No. Those are the 5-inch, 6-inch and 7-inch dampers for larger boilers. Match the damper to your boiler's flue connection diameter and model.
  • What if only the harness or actuator is bad? Weil-McLain lists the vent damper harness 591-391-795 and the vent damper actuator 510-512-337 as separate service parts. Replace the full 381-800-474 assembly when the body, blade or several components are damaged.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.