McDonnell & Miller 51-S-2 Switch R-22 Enhanced Durability: Engineered to handle

Enhanced Durability: Engineered to handle the thermal fluctuations and moisture typical of high-efficiency condensing furnaces

Engineered for high-performance HVAC platforms

The 180-degree "pigtail" design is optimized for vertical orientation to ensure the condensate remains trapped in the bottom of the loop

utilizing a genuine Lochinvar rubber door gasket ensures the unit meets its original factory specifications for airflow and thermal containment

McDonnell & Miller 51-S-2 Switch R-22 Enhanced Durability: Engineered to handleThe McDonnell & Miller 51 S 2 is a heavy duty mechanical water feeder and low water cut off (LWCO) designed for low pressure steam and hot water boilers. Engineered for systems with a maximum vessel pressure of 35 psi, this unit features a snap acting SPDT switch that ensures positive electrical contact for burner control or alarm signaling. The 1" NPT connections allow for straightforward integration into existing boiler piping, providing a reliable