That's right but if the boiler was at its rated output of 30kw then the HW temperature would be almost 39C (38.6C). If you required a bath filling temp of say 45C then you would have to reduce the flowrate to just under12LPM (11.94) again assuming boiler at its rated 30kw output.
Central Heating Max. Output 21.2 kW Mounting Wall Mounted Flow Rate 12.2 l/m
If I was to fill a bath at 14.52lpm does that mean the bath would be 31.8c ?
I think I'll have to get the installer back in the new year for further investigation.
The 21.2kw output above is the output when on CH duty only.
If you like sometime you might take one more test of that bath flowrate and temperature and also the cold mains temperature to really tie down the actual boiler output very accurately.