McDonnell & Miller

A Century of Boiler Safety Engineering

McDonnell & Miller has been one of the most trusted names in boiler safety and control technology for over 100 years. Founded in 1924, the company was born out of a simple but urgent need: to make steam heating boilers safer and more reliable. From its earliest automatic water feeders for low-pressure steam boilers to the sophisticated electronic controls used in today's commercial and industrial systems, the brand has never wavered from that core mission.

Now operating as a Xylem brand, McDonnell & Miller has pioneered innovation in boiler safety for industrial, commercial, and residential applications across more than a century of continuous operation. The company holds ISO 9001 and ISO 14001 certifications, reflecting a long-standing commitment to quality manufacturing and environmental responsibility.

What McDonnell & Miller Makes

At the heart of the McDonnell & Miller catalog are boiler safety controls and aquastats — devices that monitor water level, temperature, and pressure to keep boiler systems running within safe parameters. Their legendary low water cut-off (LWCO) devices, available in float-operated and probe-type styles, automatically shut down the burner when water drops to a dangerous level, preventing catastrophic dry-fire failures. Series like the 150S and 157S have become industry standards in commercial boiler rooms nationwide.

Beyond LWCOs, the brand produces a broad range of float switches for liquid level sensing applications — from cooling towers and storage tanks to water fountains and process equipment. These float-type controls are engineered for reliable, precision operation even in demanding environments.

For technicians maintaining hydronic systems, McDonnell & Miller offers zone valves and hydronic heating parts, including relief valves designed to protect tanks and hydronic circuits from over-pressure conditions. Their boiler control boards and modules — including probe-type electronic LWCOs like the PSE-800-M series — bring modern electronic precision to boiler monitoring and pump control. And for anyone keeping older equipment running, McDonnell & Miller's line of boiler repair parts covers everything from probes and paddles to castings, gaskets, and head mechanisms, making it easy to restore controls to factory-spec performance without full replacement.

Why Engineers and Technicians Trust McDonnell & Miller

• 100+ years of proven field performance across residential, commercial, and industrial boiler applications
• Float-operated and probe-type technologies to suit low-pressure and high-pressure steam and hot water systems
• Wide application range — from small residential boilers to demanding oil, gas, and petrochemical process systems
• ISO 9001 and ISO 14001 certified manufacturing for consistent quality and environmental stewardship
• Extensive repair parts availability to extend the service life of installed controls

Whether you're specifying controls for a new installation, performing routine maintenance, or replacing a failed safety device, McDonnell & Miller products offer a depth of engineering heritage that's hard to match in the boiler controls industry.