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My thermostat has reached its set temperature, but the electric heater is still running.

An electric heater can continue to run for a short time even after the set temperature has been reached. To better understand why this happens, it helps to first be aware of two key features of smart thermostats, namely temperature ramp up and temperature hold.

Temperature ramp up

When you raise the set temperature of a thermostat by several degrees at once, there can be a noticeable difference between the set temperature and the room temperature. When this happens, the thermostat will run the heater at maximum strength until the room temperature is 0.5 °C below the set temperature, then reduce its output. On occasion, the room temperature might exceed the set temperature; this is what’s known as “overshoot” (and it’s completely normal).

In cases of overshoot, the screen on your smart thermostat will display both the heating power indicator and a temperature that is slightly above the set temperature. You will also notice that the thermostat tile in the Hilo app will indicate that it is still heating, but not at full capacity.

Overshoot can be compared to accelerating from 60 km/h to 100 km/h in your car; you might end up driving slightly faster than 100 km/h at first, but then you can take your foot off the gas to reach a steady 100 km/h.

Temperature hold

When a thermostat’s set temperature is reached, you would expect that the thermostat display show no heating power indicator and that the thermostat tile in the Hilo app be grayed out with a zero watts display. And for a while, this would be the case. But a smart thermostat is designed to keep the set temperature as constant as possible. For this reason, it’s perfectly normal that the thermostat, even if it senses a room temperature equal to the set temperature, continue to heat the electric heater to a specific power level. Meaning that, in some instances, your electric heater will continue to heat up a little, and the thermostat’s set temperature might be exceeded by 0.5 °C to 1 °C. This is a normal occurrence that is controlled by the thermostat algorithm.

Let’s go back to the example of driving your car at 100 km/h. To maintain this speed, you have to keep your foot on the gas. Sometimes, however, you’ll end up going slightly faster than 100 km/h and will have to adjust the pressure on the gas pedal accordingly.