No echo Terry, but I'm of the opinion that if the original points aren't answered, then repeating the suggestion eventually gets to the bottom of the problem.
We now have a nozzle size which reinforces our several suggestions of over aired start up. We now also know that the boiler has a direct air feed from outside, which I have encountered in the past where you can get a howling gale direct into the fan, (and also mice, ask me how I know) without any 'tempering ' as you get on true balanced flues, and also a draw off the conventional chimney.
I see very few Heating Worlds around here and avoid them if possible.
There is one I have repaired with an electrically operated flue damper .
I think that is HW.
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