The water pressure sensor is designed to measure the water pressure in the heating system.
The principle of operation of the relay boils down to the fact that if there is not enough water or there is an air plug in the heat exchanger, the low water level relay sends a signal to the control unit and the boiler is automatically turned off.
The sensor has a 1/8 threaded connection, a pressure of 0.2-1.2 bar and three mounting contacts, but two are used.