What is the function of the Tank Sensor?

The Tank Sensor is wired in series with your existing hot water cylinder thermostat. A connected digital temperature sensor probe is fitted to the how water cylinder - this allows the hot water to be controlled to different temperatures at different times of the day. Operationally the Tank Sensor also replaces your hot water programmer / time clock, this becoming redundant and is either removed and linked through or set to "always on".