Really interesting Mick @Zarch
It reinforces what I thought, and what I tried to convince OVO of at the time, but they weren’t having any of it, I have a thread on my pump where we could dig in to the heat loss subject if you are interested.
I think the pump is big enough in the monobloc outside, it can draw 100w. The far rad in the playroom does get warm, just not as warm as others.
I can’t adjust the flow rate of the pump, but I can alter the target deltaT. I wonder if I target dT 7 whether that would help. Reading the heat geek link on pipe sizing this suggests I can get more heat output, but I wonder what the compromise/effect will be? Maybe something to try out over the weekend.