It depends - no harm in trying lower temperatures. I’ve got lots of radiators and so rarely exceed 40C.
Thanks for highlighting the lower running power Simon.
I was previously running with a minimum flow temp of around 36C as the 900W minimum power meant it didn’t seem worth going lower in our system. For the past few weeks, I’ve experimented with minimum flow temperatures of around 32-33C, and am seeing power usage in the 850W range.
Hard to say what the efficiency impact is, as I figure with higher flow temps more heat would have been transferred to the house and so system would have shut off sooner.
I am hopeful that in cold weather I might be able to run system overnight at low-30s C to try and stop house getting too cold, while also getting decent COP and having fewer defrosts than at 36C (or higher) flow temps.
It’s interesting to see a manufacturer improve installed products like this - especially when it involves a costly engineer visit… (feels like there must be something more to it 
)