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These boilers need a high flow rate to correctly ignite and modulate properly, if you look in the manual it actually states equivalent of about 1600 l/hour flow rate minimum. The head loss across the boiler alone at that flow rate is just over 4m.
They don't like variable speed pumps as they are not in control of them, you tend to get better performance off these boilers having pump at a fixed output.
Part of the issue is people quite often "over specified" this boiler, as in used it where a much smaller unit would have worked, The burners obviously do modulate, but they need to flow enough water to ignite, test the sensors, then modulate to what they need, which takes about 30-60 seconds going between 60-100% of full power regardless of what its range rated to on D.0
Unless youre 13 radiators are all 2 meter long double panel double finned units, then theres a fair chance the boilers bigger than it needs to be. However it's not that much of an issue so long as you provide it with plenty of flow rate.
I'd be tempted to set you're output to winter output, fix the pump speed, and when its running at the fixed output use D.40/41 to gauge the difference between the flow and return and try get the pump speed to a point that gets you around 10-15 degree difference on the radiators, then run the DHW on its own and if it holds between 5-20 degree difference without cycling then you should be good.
They don't like variable speed pumps as they are not in control of them, you tend to get better performance off these boilers having pump at a fixed output.
Part of the issue is people quite often "over specified" this boiler, as in used it where a much smaller unit would have worked, The burners obviously do modulate, but they need to flow enough water to ignite, test the sensors, then modulate to what they need, which takes about 30-60 seconds going between 60-100% of full power regardless of what its range rated to on D.0
Unless youre 13 radiators are all 2 meter long double panel double finned units, then theres a fair chance the boilers bigger than it needs to be. However it's not that much of an issue so long as you provide it with plenty of flow rate.
I'd be tempted to set you're output to winter output, fix the pump speed, and when its running at the fixed output use D.40/41 to gauge the difference between the flow and return and try get the pump speed to a point that gets you around 10-15 degree difference on the radiators, then run the DHW on its own and if it holds between 5-20 degree difference without cycling then you should be good.