Technavate Ao Smith Geyser Thermostat ( Match And Buy ) Temperature Sensor and Controller Electronic Hobby Kit ()

The thermostat decides when the element switches off. Fitting one is quick, but it sits at mains voltage right next to the element terminals.

1. Switch off at the geyser switch and the MCB, and let the tank cool.
2. Drain the tank only if your thermostat is immersed. Many are surface or pocket-mounted and need no draining — check before you empty it needlessly.
3. Remove the cover plate and photograph the wiring, including which terminals the element leads occupy.
4. Note the probe depth and position before you pull the old one — a probe not pushed fully into its pocket reads cold and lets the water overheat.
5. Fit the new thermostat to the same depth, in the same clips, and reconnect exactly as photographed.
6. Set the temperature sensibly. Around 55–60 °C is hot enough for domestic use, scalds less readily, and scales far more slowly than a maximum setting.
7. Refill if you drained, then restore power and watch one full cycle: the element should switch off at temperature rather than running continuously.

If the new thermostat never cuts out, switch off at the MCB — a thermostat that cannot switch off is what the thermal cutout exists to catch, and it should not be left running.