What flow temperatures are you currently running?

Especially when the actuators are down: Check if the square nut underneath is completely unscrewed. I recently discovered that the flow was throttled on both the supply and the return. Lo and behold: 20% less pump power needed for the same flow.

More than 5 l/min —> 300 I don't see there.

Those are just estimates, read from the wrong perspective of a photo. I trust the flow meter of the UWP more.

These are our values at about 10°C outside temperature.
The insulation standard is KFW55.

A small buffer tank is available with 18 liters capacity as a return series storage.

The actuators have their own fuse, however, all the actuators are cramped into a junction box with Wago terminals. I need to take my time to unravel everything and then disconnect, so for now, they are all manually set to max or permanently open.

The actuators have their own fuse, but all the actuators are crammed into a junction box with Wago terminals.

Doesn't matter, pull the fuse, unscrew and let it dangle. I don't bother to remove them ;)

I have already done that too, but it’s still annoying during fine-tuning when those things are dangling around. The final goal is actually to completely disconnect them and banish them from the distribution box.