Description
The Xylem-McDonnell & Miller 157S-M (Part Number 175402) is a combination low water cut-off and pump controller engineered to protect steam and hot water boilers from the hazards of low water conditions. Featuring a snap-acting manual reset SPDT (Single-Pole, Double-Throw) switch, this control provides reliable boiler protection by shutting down the burner when water drops below a safe operating level — and requires a deliberate manual reset before the system can resume operation, adding an important layer of safety accountability.
McDonnell & Miller, a trusted name in hydronic and steam boiler controls for over a century, designed the 157S-M for straightforward installation and dependable long-term performance in commercial and residential boiler applications.
Key Features
- Combination low water cut-off and pump controller in a single unit
- Snap-acting manual reset SPDT switch for positive, reliable switching action
- Manual reset design requires deliberate operator intervention before restart — enhancing boiler safety
- Float-operated mechanism provides accurate water level sensing
- Suitable for steam and hot water boiler applications
- Side-mounted installation for easy integration into boiler piping
- Durable cast iron body construction for long service life
Product Specifications
- Part Number: 175402
- SKU: 157S-M
- Switch Type: SPDT (Single-Pole, Double-Throw), Snap-Acting
- Reset Type: Manual Reset
- Function: Low Water Cut-Off / Pump Controller (Combination)
- Brand: Xylem-McDonnell & Miller
Applications
- Steam boilers requiring low water protection and pump control
- Hot water boilers in commercial and residential heating systems
- Hydronic heating systems requiring automatic pump sequencing
- Installations where manual reset capability is required by code or preference
Why Choose the McDonnell & Miller 157S-M?
The 157S-M combines two critical boiler safety functions — low water cut-off and pump control — into one compact, reliable unit. The snap-acting SPDT switch ensures clean, positive switching without hesitation, while the manual reset feature prevents automatic restart after a low water event, protecting both the boiler and building occupants. Backed by Xylem’s engineering expertise and McDonnell & Miller’s century-long legacy in boiler controls, this unit delivers the dependability that HVAC professionals and building engineers demand.
