Hydrolevel low water cut-offs are electrically operated. A probe is installed in the boiler shell or external manifold and is connected to the control unit. Water is used as a conductor to complete the circuit between the probe and the boiler shell. When water is in contact with the probe, the circuit is completed; when the water level drops below the probe, the circuit opens. Hydrolevel controls provide contacts to de-energize the burner circuit in a low water condition. Shorter probe for mounting in standard reducing tees.