@Wayne-TP I mean that if I set the temperature of the thermal head to 20 degrees, it will close, for example, when it reaches 19.5 degrees, then it will turn on, for example, at 19 degrees to heat again.

  @Wayne-TP Thank you for the explanation. I thought that when the temperature is set to be 20°C in the room and it drops to 19°C, then it starts, for example, it rises to 20.5°C and the valve closes.

  @Jirinak82 Hi, in my understanding, this KE100 thermostat works on principle of continuous regulation, where the valve can be open in a range from 0% (closed) to 100% (fully open). Your question was based on your understanding, that the valve is either fully closed or fully open, where the term hysteresis makes sense. So think about it this way.. 

  @Marian1972 Thank you for the answer. Unfortunately, it is a bit incomprehensible. I did not say that it is not fully closed or open. I asked how hysteresis works with the thermovalve. You probably know what hysteresis means. It must also be set here. But no one knows how.

  @Jirinak82 

My observations do not match what Wayne says. When TRV is in ON (idle) status and measured temperature is above set target, it looks like the valve is fully closed. Otherwise I would have heard or felt the hot water (barely) flowing through the radiator and immediately returned all TRV's. When it's open, the status changes to ON (heating) and the Tapo app also reflects that. I found no way to check the actual % value but it likely is variable.

Regarding hysteresis, it cannot be changed in the app, but you may switch the TRV to "night mode". It claims the valve will not move as often so my understanding is that it should mean higher temperature fluctuations.

After couple of days with my KE100 + T315 I can say I'm a bit disappointed on how they approach temperature control.

It seems like the hysteresis* and proportional valve controll needs some adjustments. For now I can observe an annoying approach:

- temperature drops below set (e.gt. set is 22, current is 21.7) - valve opens, but too much in my view

- temp fairly quickly gets to 22.0 -> valve shuts down - wrong again, it should close a bit (say 50% less)

- of course the temperature will drop again, and the vale soon opens again...

- that might also be the reason why these vales tend to keep a temperature lower than set (for example,. in my bathroom, it will never reach the set 25C, it's at best at 24.5) - why? The algorithm is flawed, it "panics" and shuts down too quickly, instead of applying proportional adjustment. It seems to have an issue with these "low open states to maintain temperature" - like valve opened at 10 or 20%)

When I had a standard thermostat, it would just keep the heaters at warm temperature and the system would "stabilize"

If the temperature outside does not change, KASA / KE100 should be able to stabilize the temperature by finding correct valve position to maintain the temperature, rather than fighting back and forth. When I check the radiator, its either hot or cold. While it could easily be open at 20% the entire night. 

On the other hand I must say the temp on the T315 is really close to the set one, but it does fluctuate, and does open/close the vale all the time, rather than gradually adjust it to correct "open" position. 

@Wayne-TP could you please discuss this with KASA dev team? 

I will also try if the "Night mode" - that seems to be more relaxed hysteresis* profile and see if it does the trick. 

Now the valves give an impression to either fully open or close (that why I would love to see that information somewhere - how much is it open?)

(*Hysteresis in an automatic heating regulator or valve refers to the built-in buffer range around the target temperature. Instead of constantly switching on and off as soon as the temperature changes slightly, the system waits until the temperature moves a set amount above or below the target before it adjusts. This helps to prevent rapid cycling, reducing wear on the system and improving energy efficiency.)