Hydrolevel Safgard 650 Commercial Hot Water Boiler Low Water Cut-Off 120 VAC EL1214-P 3/4" NPT Probe The Safgard Commercial Boiler Low Water Cut-Offs are used as the primary low water cut-off on residential and commercial water boilers. Hydrolevel controls utilize a non-moving heavy duty electronic probe to sense liquid levels. The probe can be installed in an equalizing line or directly into a boiler or water tank in accordance with manufacturers' instructions and local and State codes. When water is in contact with the probe it completes a circuit between the stainless steel probe tip and the tank or boiler surface in which the probe is installed. When the water level drops below the probe the circuit opens. Hydrolevel low water cut-offs for hydronic heating systems use the water signal to allow the burner to operate. If the water level drops below the probe the circuit opens and the cut-off shuts down the burner.[]