Forgive linear approximations for simplicity:You haven't answered my last question.
How do you work that out?1200 litres/hour
So at 70°C flow, the total output drops from 11 kW to 8 kW and the difference across the radiator drops to from 11°C to 8°C.
900 litre/hour, flow 85°C, boiler power 11 kW:
11000/(900/3600*4187) = 10.5°C temperature drop
Combine this with a rated mean temperature difference of 60°C and we get flow and return temps around 85°C and 75°C
Drop the boiler output to 8 kW:
8000/(900/3600*4187) = 7.6°C temperature drop
naughty approximation: 60°C mean difference for 11 kW scale:
60*8/11 = 43.6°C mean difference => 63.6°C mean temperature
67.4°C flow and 59.8°C return
OK not quite 70°C - 62°C but not so far out.