So, just to see what happens I changed my emitter to underfloor at about ~11AM.
I then dropped the DeltaT to 5 and increased the overshoot to 4.
It seems to have settled down for now.
This is on external control via my Tado at the moment.
I will have to keep an eye on rooms temps to make sure everything stays warm.
If it stays stable I will switch it back to pure WC later, maybe drop the overshoot and increase the DeltaT and see which causes it to start cycling again.
I sometimes see the same behaviour after hot water cycles where the water temp in the volumiser is high compared to the required flow temp for heating but that settles down once the flow temps return to normal.