Heating, something is wrong here. Hallway always 22°..

First of all, I would first carry out a thermal balancing and adjust the heating curve accordingly. THEN everything else can be considered.

I think I just expressed myself a bit unclearly. We have a house on a slope, ground floor and basement. The hallway on the ground floor has only one window, frosted glass, facing north, where the front door is. The hallway downstairs has the terrace door, which faces south.

Still not fully understood without a floor plan. Are the two hallways connected by the stairs? Or is it closed off (with doors)?

The sun always seems to shine strongly against it in the afternoon, that’s true. But can that be responsible for the heat in the hallway in October? Even at night?

Of course. As I already wrote. The sun blasts in, warms the air and also the floor, and if it’s long enough, also the screed (+ walls, furniture, etc.). That stores the heat and radiates it out even at night.

Yes, we do have a ventilation system. But the hallway is not connected to it.

That’s not a problem; hallways are often planned that way. Then you have supply air in the bedrooms and exhaust air in the bathroom. The air should then, if properly planned, flow from the bedroom through the hallway into the bathroom. The prerequisite is that the air can circulate. So you shouldn’t have sealed doors.

And yes, I would also perform a check as suggested. Still, I would want to know where which temperatures are. Because even if a 1 - 1.5 degree difference is noticeable, your descriptions sound more like significantly more.

the floor in the hallway should be warm

I wouldn’t completely agree with that. I would always go by the room temperature regarding how "warm" it feels.

Warm in the sense that you can really feel it on your feet is probably more the case in the more closely laid heating circuits like the bathroom.

I would check how the valves in the distribution respond or just have the plumber come and go through it together to make sure it matches the calculation.

The hallway on the ground floor, our front door faces north. In the basement, the large terrace door is on the south side, the sun shines on it during the day.

The hallway downstairs has the terrace door that faces south. The sun always shines strongly on it in the afternoon, that's true. But can that be responsible for the warmth in the hallway in October? Even at night?

Heat rises. Maybe it just accumulates in your hallway?

As immediate assistance, it is advisable to keep the bathroom door on the upper floor open; heat rises upwards and the bathroom will warm up. Until the hydraulic balancing is done.

At 22°, talking about running into a wall (vs 20-21° in other rooms) also seems astonishing to me. So measuring the status quo again with thermometers doesn't sound wrong to me either. (Perception is subjective, but for me, it takes significantly more temperature for that.) Otherwise, I don't have much to add that hasn't already been said. E.g. floors and such retain heat well in newer buildings, so shading might also be considered in the south. Further checking the heating also doesn't sound wrong.