The Vaillant flow sensor is designed for use with Guernsey/Jersey only (condensing), Ecotec VUI (condensing) and Ecotec VUW (condensing) boilers. The sensor decreases circuit resistance in line as the temperature increases. The boiler's printed control board sends a current to the thermistor, deciding whether a decrease or increase in heat is required by reading the relative resistance.

• Comes with clip