So the big question is, did you awake soaked in sweat at 03:00 because you'd turned all the tstats up to full, or did you awake because you were freezing (because I forgot to mention that turning the other two tstats down was just a temporary measure to see if the other rad was working properly or not)?
No, it does not. I did some more google searches and found one identical problem mentioned by someone. They say the problem could be something related to the valve (e.g. not correctly set, etc). I'll call the hauswartung(?) people I guess.
If the cold half is where the usage meter thing is then you might want to leave it ;-)
By the way, while a thermostatic controlled device is normally on/off that isn't always the case with a TRV. Some won't open fully when there's not much temp difference and indeed opening to full will bring the rad up to temp quicker. Doesn't work in my car though when my gf sets the a/c to 17C to make it cooler :-)
I only say it as a bit of a tongue-in-cheek comment because if the counter is on the cold part you'll be paying less for the heating that you are getting on that radiator.
I've never seen a rad without a bleed valve but I guess there could exist such a valve with it all combined. I have however seen radiators overpainted so much that you coudl easily not detect that there's a bleed valve there. Otherwise the approach could be to split the connectors somewhere at the top but it's not something I'd recommend in a rented apartment.
Overpainted!!! I used the flashlight (with a little angling) and I saw that small circular trace of the bleed valve. A keen-eyed one could have spotted that in seconds though. You saved me from reading that agonizing Danfoss manuals. Many thanks.
This thread has me thoroughly inspecting the radiator in my kitchen. Yet no amount of searching leads to the discovery of the valve for bleeding. Maybe your eyes are keener than mine.
That is what I assumed since that is where ALL our other radiatoer have their valves. But I can't find anything. Oh well, I presume that by bleeding all the other radiators any air caught in this one in particular is released as well. After all, it is one circle, right?
I've seen a few old systems which originally only had plain valves rather than thermostats, only the rads on the top floor had bleeders. More accurately, only the topmost rad on a riser had a bleeder. They were all cast Iron rads though - yours looks more like '60s era.