@Wayne-TP I'm not directly controlling the valve so I don't know for sure if it is 100% closed, however I can hear that there is no water passing through the radiators when approaching the target temperature. If I increase the temperature be one degree I can hear the valve open and water passed through the radiator. Sometimes if I manually increase the temperature on the TRV itself I can see that the icon to indicate that the valve is open is not visible, once temperature is increased the icon becomes visible. 
 

I have the TRVs connected to Home Assistant and I'm using a smart switch in place of my old thermostat to control the boiler. I have an automation that uses the switch to call for heat from the boiler when the TRVs enter into heat(heating) state. 
 

Smart Control is disabled and I'm now using a schedule within Home Assistant to control the TRVs. This issue was present when I used to the Smart Control feature in the Kasa app, changing to the schedule in Home Assistant has made no difference. 

Good example of this issue:

The temperature in room dropped to 20.9, target temperature is set to 21. TRV entered heating mode and has been in heating mode for 20 mins however the radiator is still stone cold. The TRV valve is closed but still calling for heat. 
 

Is it possible to add a way to adjust the hysteresis? Set the TRV to come on when temperature drops 0.5 degrees below the target temperature, then turn off when room reaches the target temperature. Either that or set a minimum value open percentage so the radiator always heats up when calling for heat?

  @SC92 sorry to disappoint you, but these valves:

- do not show real open / close state (not to mention position of the valve in %). ON/OFF state is something different. 

- they have the most flawed temperature control among all valves I have used: they can never stabilize, they will "fight" by irrationally opening or closing entirely

- the "heating" status that you see in the history simply indicates if the temperature was below (on) or above set (off), it has nothing to do with the vale being open or not. 

- it's "normal" for these vales to see a situation, where you get e.g. 23 set, 22.8 in the room, and they shut down entirely. It's annoying, and creates a thermal discomfort, as even though the temperature is close to what was set, in winter time you want the system to stabilize and keep water flowing at some amount, like 15, 30, 60% or whatever. 

If you want, you can check my thread about it https://community.tp-link.com/en/smart-home/forum/topic/843496

and my original thread.... https://community.tp-link.com/en/smart-home/forum/topic/715030

12 up-votes, 5000 views, and TP-link support saying "yeah yeah we know it does not work, and we will maybe fix it one day" - no they did not for the last 12 months. 

If you agree, please send a support ticket from within the app.... maybe TP-link will eventually decide to spend 50$ on fixing this firmware issue. 

oh, I have even found a response I got from the support:

TP-link support:

The heating process controlled by KE100 begins with opening the radiator valve. When the temperature approaches the target value, the valve opening decreases, and once the target temperature is reached, the valve closes and stops heating.

This shows they have no idea how a typical smart valve works..... WHY (!) would it close when the temperature is reached?! Guess what will happen next!? temperature will start dropping again, unless no heating is really needed. 

Good luck with your automation!

/ Mike