mmmm....
Heatline B rated boilers now have variable fans. there is a halls effect sensor on top of the fan it could be the wires off that hitting the fans cooling fan(yes the fan has a fan)
I have had one doing this. it was on a Heatline boiler that I fitted so knew straight away that it was not right. your installer may not have this insight I just thought it was a loud boiler.
Heatline B rated boilers now have variable fans. there is a halls effect sensor on top of the fan it could be the wires off that hitting the fans cooling fan(yes the fan has a fan)
I have had one doing this. it was on a Heatline boiler that I fitted so knew straight away that it was not right. your installer may not have this insight I just thought it was a loud boiler.