Thank you for the calculations they are very handy.Yes, the table gives (presumably) burner output, the only assumption that will marginally affect the boiler output is its efficiency so 85% to 92% should cover it, the calculation for pressure is universally used, ie flow is prop to the sq.root of pressure, I should have shown that as ^0.5 and not ^2, but I did use ^0.5 in the calculation.
Can't really comment on that by pass except to suggest finding out exactly where the connections are teed in.
I am totally stumped over the whole system 😂😂😂 but have quite a bit more knowledge now thanks to you.