The underfloor heating on the first floor is no longer working

Yes, here with me in green.

As you can see in my pictures, we haven't connected the electronic actuators at all for financial reasons.

So the pump capacity is too low

From the circulation pump?
Can't that be measured?
Errors or similar in the system are definitely not displayed

When I look at the blue caps, it looks different on the ground floor and basement than on the upper floor. (Distance from the bottom edge of the cap to the distributor) While those on the ground floor and basement appear to be fully screwed tight, those on the upper floor look loose. Are there valves hidden underneath?

Yes, under the blue caps are usually the regular valves.

Then that would be the explanation: turned in = open and turned out = closed

When I look at the blue caps, it looks different on the ground floor and basement than on the upper floor. (Distance from bottom edge of the cap to the distributor) While those on the ground floor and basement appear to be fully screwed on, those on the upper floor look loose. Are there valves hidden underneath?

Yes, they are different now, that's because some burst, they were all actually blue and round with the notches on top, I simply screwed on others because the old ones were no longer there, but it worked before, only not since yesterday, and these white ones are the electric or electronic actuators which we never connected for financial reasons, If you turn the caps to the right, the heating should run, it worked that way for the last 19 years.