This should mean IMO that the flowrate through the boiler is 1.0 m3/hr, 16.7LPM, so if the boiler has its own internal pump capable of pumping far more, the flowrate is being throttled/controlled by this relatively small pump, running the pump on full CP mode (knob fully right) or setting it to C3 should give ~ 1.4m3/hr at 4M head & 20W which may help the boiler fire up for longer than 11 secs and not reach SP+5C for a few minutes depending on the heating load.
Post 26 showed a dT of , 53-38, 15C, if the primary flowrate is consistent at 1m3/hr, 16.7LPM, then the boiler output was 17.5kw but if it was only just above minimum of say 12kw then the flowrate was only 11.5LPM?.
Another way of checking the primry flowrate is to take the dT and read off the % firing like in post 30 where 19% was presumably the boiler output then, 9.3kw??.
Also, if 16.7LPM is the flowrate through the boiler then the output at a dT of 20C is only 23.3kw, I think the max design flowrate through boilers is based on this 20C dT which means one should be able to circulate 35.1LPM, 2.1m3/hr.
What exactly I wonder is the role of the LLH in your setup as I thought that the primary side dealt with the heat source and the secondary side with the heating demand, the output from the boiler flow is teed off to the heating before the primary (as well as feeding it).
Are there any (other pumps) associated (apart from the UFH manifold pump) with the LLH secondary side?,