With a name like "big banana" it makes me wonder id you are the kind of person who would increase the power input above what the manufacturer has specified.
I went to a gas boiler tonight with a burner pressure of 16 when the maximum should have been 10.5
There is no point in having a manual to make a pointless change. You have not established the need for increased output. All heating systems (even if designed correctly) only work near their maximum for 11 days per year, the rest of the time they are oversized. Unless your boiler runs without ever the control stat opening, then it has more than enough output. Those particular boilers are frequently underloaded.
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