McDonnell & Miller 6667 Control

The McDonnell & Miller 6667 (Part Number 153825) serves as a critical mechanical low water cut-off head mechanism specifically engineered for steam boiler safety. Designed for systems with a maximum steam pressure of 20 PSI, this replacement unit ensures reliable burner circuit interruption if water levels drop below the safe operating line. As a float-operated control, it utilizes a manual reset functionality, which is essential for compliance in jurisdictions requiring manual intervention after a low-water event. This mechanism is the direct replacement head for Series 67 and Series 767 controllers, making it a standard component for hydronic heating maintenance and boiler safety upgrades. The heavy-duty bellows seal prevents leakage and ensures consistent float movement, while the dual switch configuration allows for simultaneous burner shutdown and alarm or electric water feeder activation. Integrating this M&M 153825 head mechanism maintains the integrity of the pressure vessel while providing low water protection.

Technical Specifications & Benefits

• Compatibility: Direct replacement head for Series 67, 677, and 767 low water cut-offs.
• Operational Rating: Specifically rated for 20 PSI max steam pressure applications.
• Switch Configuration: Includes a No. 2 Switch for burner control and supplemental alarm signaling.
• Mechanical Reliability: Features a robust float mechanism designed for longevity in harsh steam environments.
• Safety Compliance: Manual reset design prevents automatic burner restarts, ensuring system inspection after low-water conditions.

Common Installation & Service Questions

Can the 6667 head be used on hot water boilers?
While primary low water cut-offs are often associated with steam, the McDonnell & Miller 6667 is specifically optimized for 20 PSI steam systems. For high-pressure hot water applications, consult the specific PSI ratings of the Series 61 or 63.

Does this unit include the float housing?
No, the 153825 is the head mechanism only. It is designed to bolt onto your existing Series 67 or 767 housing, allowing for a faster boiler repair without disturbing the system piping.

How do I wire the 6667 to an electric water feeder?
The internal No. 2 switch provides terminal connections for both the burner circuit and a separate line for a McDonnell & Miller Uni-Match or similar electric water feeder to maintain appropriate boiler water level automatically.

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.