McDonnell & Miller 63-M Low Water Cut Off

The McDonnell & Miller 63-M (Part Number 143100) is a heavy-duty, float-operated mechanical low water cut off designed for superior reliability in both hot water and steam boiler applications. Built for contractors who require a dependable safety interface, this unit features a manual reset mechanism and a robust No. 2 dual-switch assembly. These switches provide simultaneous low water cut-off protection and a dedicated circuit for an electric water feeder or external alarm system. With a 1" NPT connection and a maximum boiler pressure of 50 PSI, the 63-M is a staple for residential and light commercial hydronic systems. The large float chamber reduces the impact of surging water levels, while the packless bellows ensure a leak-free seal between the internal mechanism and the electrical housing. For hot water systems, integrate this control with a TC-4 test cock to meet local inspection codes and ensure proper blow-down functionality.

• Dual-Switch Versatility: The integrated No. 2 switch allows for independent control of the burner circuit and a 120V boiler water feeder.
• Manual Reset Safety: Prevents automatic burner restart after a low water condition, requiring a technician to inspect the system and manually depress the reset button.
• High Pressure Rating: Rated for a maximum boiler pressure of 50 PSI, making it suitable for a wide range of low-pressure steam and hydronic boilers.
• Durable Construction: Heavy-duty brass and stainless steel internal components resist corrosion and provide long-term mechanical LWCO performance.

Can the McDonnell & Miller 63-M be used on hot water boilers?
Yes, the 63-M is designed for both steam and hot water applications. When used on hot water systems, a TC-4 test cock is recommended to facilitate periodic testing and blow-down.

Does this unit include the replacement head gasket?
Standard installations of the 143100 include the necessary housing components; however, when performing maintenance, the CO-12 head gasket should be inspected and replaced if necessary.

Is this a direct replacement for the standard Series 63?
The "M" designation indicates a manual reset LWCO. While the physical 1" NPT mounting and 50 PSI rating are identical to the standard Series 63, the manual reset feature is a specific safety requirement for many commercial jurisdictions.

This item is not eligible for free shipping.

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.