ᐅ Room with underfloor heating feels freezing cold

Hello, the house was completed in 2015. We have underfloor heating. I just got a shock when I opened the playroom. It was freezing cold, including the floor. All the other rooms are warm… I opened the manifold box. For each room, there are these small tubes like those used for measuring water levels in plants. The tube for this room is at the very top… Could it be because of that? Can I do anything myself, or should I call the plumber? For now, I turned up the thermostat in the room...

The actuator might be broken; we have encountered this before.

I’ve checked now. They are the Tascosetter. The room in question is set to over 2 liters (0.53 gallons) at the full stop. Could this be related? And can I adjust anything here myself?

The tubes probably indicate the water volume, which is needed for the hydraulic balancing.

Hello, I have now set the room to the maximum. Now it is getting warm. Hmm