Low Water Cut-Off with Manual Reset

McDonnell & Miller Mechanical Low Water Cut-Off – Proven Safety for Steam and Hot Water Boilers

The McDonnell & Miller mechanical low water cut-off is a float-operated device engineered to prevent boiler operation under unsafe low water conditions. Designed for use in residential and light commercial steam or hot water systems, this control offers dependable performance without relying on electronic components, making it ideal for environments where mechanical reliability is preferred or required by code.

Mechanical Protection for Critical Boiler Safety

This low water cut-off uses a precision float and switch assembly enclosed in a durable chamber to sense water level. When water falls below the minimum safe level, the internal switches break the circuit to the burner and/or activate an alarm, helping to prevent dry-firing and catastrophic system damage. With a manual reset option and dual-switch capability, this unit supports both safety shutdown and alert notification.

Key Performance Features

• Float-Type Mechanical Operation – No external power source required for actuation, ideal for dependable, fail-safe performance.
• Dual Precision Switches – Independent switching for burner shutdown and low water alarm applications.
• Large Float Chamber – Improves level sensitivity and extends control life under continuous use.
• Quick Hook-Up Fittings – Simplifies installation into standard piping configurations.
• Manual Reset Option – Meets jurisdictional requirements for manual reset on critical boiler applications.

Specifications

• Max Pressure: 20 PSI
• Electrical Rating: 3.7 FLA / 22.2 LRA at 240 VAC
• Voltage: 120/240 VAC
• Switch Type: SPDT or DPDT (model dependent)
• Connection Size: 3/8” NPT
• Mounting: Standard side-tap installation
• Warranty: 1 year from installation date / 2 years from manufacture

Installation Guidance

Although this unit is straightforward to mount mechanically, proper setup requires attention to boiler piping orientation, blowdown procedure, and electrical interlock with the burner circuit. Installation should be performed by a licensed technician to ensure compliance with local mechanical and safety codes. Use of blowdown valves is recommended for maintenance access.

Contractor Insights

Professionals rely on McDonnell & Miller mechanical cut-offs for their field-tested durability and minimal maintenance requirements. The dual-switch configuration supports flexible wiring options, while the mechanical float ensures control even in settings where electronic sensors might fail due to water quality issues or electrical interference.

Protect Your System from Dry-Fire Damage

Mechanical low water cut-offs remain a trusted safeguard in boiler protection. Whether used in new installations or as a retrofit to replace aging components, McDonnell & Miller’s proven design ensures dependable operation and long service life.