For how long were the valves in the room @Meky? Do you think that the valves are 'stuck' at 21/22 degrees, and that they will never go any higher, or could it be that they are extremely slow in sensing temperature changes?
I'm reminded of a thread I read through on here a couple of years ago that discussed this 'lag' in perceiving temperature updates. It was regarding the thermostat (not the valves), but a seemingly very well-informed user posted a number of helpful graphs and commented that the thermostat's temperature sensor is effectively insulated by the plastic casing, which he considered a design flaw.
I wonder if a similar thing could be happening with the valves?
I found the thread, the user I mentioned even drilled holes in the casing of his thermostat to enable air to flow into the internals:
https://forum.netatmo.com/viewtopic.php?f=20&t=7373
Also in my search I came across this which may also be relevant:
https://forum.netatmo.com/viewtopic.php?f=20&t=5301