Failing all else and before you try centralheatking's remedy you might just drain down the system and refill it very slowly and keep the d/stairs rad vents cracked open while doing so, just put a few old towels underneath to catch any water while running about.
I have a combined cold feed and vent and I had to carry out this procedure once when I drained down the whole system many years ago.
Even though air is the most likely culprit, you might look at your pump again. Your pump looks as if it is pumping downwards, just check that this is correct, the pump head orientation doesn,t really matter, just that the settings are "upside down" (or maybe its just the picture that's upside down). I'm just stating the obvious but also check that the pump isolating valves are opened and that it is vented via the brass vent/degassing screw. This pump has 9 settings, 3 constant curve and 6 proportional pressure settings, it appears that you have it on PP6 which a very high setting but if there is air in the system then it won,t shift it as the pump will just ramp down. I would suggest trying it on constant curve CS2 which because of the pump head orientation is the two top solid green LEDs illuminated and a illuminated arrow (on the top) pointing to the right but you probably have tried all these settings anyway.
The international symbol for constant curve operation is a pump curve and a "arrow" for PP operation but the DAB seems to have these reversed if I am interpreting their manual correctly.