Most don't appreciate the merits of a properly trained plumbing & heating engineer , repairing boilers & installing combis is a far cry from the 'real world' of what should be expected of this trade , let most RGIs loose in a plantroom & they would be lost , ask most on here to install a bank of boilers with proper control & i can forsee a lot of head scratching.
, lets not get into ad-hoc conections , split flow & return common headers , common header with injection manifold , advantages of close coupled tee arrangements (primary/secondary) , lead lag arrangements , boiler sequencing , primary ring main with injection , correct installation of an HE boiler when added to a conventional bank , avoidance of back end corrosion , gas boosters , commercial strength testing/tightness testing , cutting threading & welding steel pipe , lead burning (herringbone/thumbnail) , i could go on........puts the plumbing & heating trade into some sort of perspective don't you think?
..................anyway , back to those clever domestic boiler monkeys on here with their fans , PCBs , flow switches...................