The Potterton Boiler sensor thermistor works by decreasing current resistance in a manner that is inversely proportional to the temperature of the thermistor. The electronic control sends a current to the thermistor and can tell whether less or more heat is needed by the resist.
Comes with O-ring
Comes with lead attached
Technical specification
TypeFlow SensorCompatible WithParamount 40 - 80Supplier Part Number986564Brand NamePotterton