The N321S is a temperature controller designed for solar water heating applications and comes complete with two NTC sensors.

It controls the water circulation system according to the difference of temperature between the two sensors mounted on the solar collector and the storage tank (or swimming pool). It offers adjustable On and Off differentials, static (T1 or T2 or T1-T2) or dynamic display (3 seconds each of T1, T2, T1-T2). It gives a change over relay output for switching the water circulation pump and provides protection against freezing (Low T1) overheating (High T1 and High T2) by allowing "override" settings which switch the output irrespective of the temperature differential, thus preventing damage to the system.