I am pleased that you have been successful after taking my advice.
To say Persimmon
"dealt with this matter very well" is incorrect.
They brushed you off and ignored your complaint until after you used the CCHB to get a ruling on your complaint - some 4 months after you posted!
If you hadn't used the CCHB-AS, Persimmon would have done absolutely nothing.
Persimmon knew they had breached CCBH requirements and were therefore given no option but to comply with the CCHB Adjudicator's ruling.
What is even more galling is that you choose to praise Persimmon, but have not given any thought to
making a donation or acknowledge that this resolution was due to the specific advice you have received on this forum.
You might be well-advised to use some of your £250 "compensation" to get your boiler installation independently checked!