Not ruling anything out.. care to elaborate? I understand dissimilar metal corrosion and that chlorinated pool water does not help that equation, but this seems awfully extreme and isolated?
I had a great article on this topic at one time that wasn't ever saved digitally so it's history.
There was a top notch boiler company that had installed a a unit in a older apartment building. They rotted the tubes out of the boiler inside of two years, twice.
They became aware they were facing a electrolysis issue but couldn't pin down the source.
Dielectric fittings (which I don't see in your images?) were not preventing their problem.
To make a long story short, they found that over many years of DIY'er type of electrical maintenance throughout the building the neutral lead had been bonded to the ground lead in many locations including sub panels and even some electrical outlets.
Bonding of ground and neutral leads can only be done at 'first strike'.
Which typically means at the main service feeding a structure and never again after that point or electrolysis is likely to occur.
Grounding rules and regulation make up the bulk of the NEC code book and the specifics bewilders MOST electricians. I've quizzed many life long electrical Journeymen and Administrators on the specifics of proper grounding of industrial equipment and steel buildings and sent them all to their NEC code book digging for answers.
Most electrical systems have grounds bonded to the water mains feeding a structure, right at those pumps is a likely location for electrolysis to occur.
It's interesting that it 'appears' your issue is limited to the one unit.
If that's truly the case you may find your problem local on that boiler, but that's rather wishful thinking.
What I would do immediately would be to ground the living schit out of the boilers chassis. I'd run some heavy copper (4/0) to a dedicated ground rod, or two. Find a good location on the boiler to bond to and grind the pretty paint off that brand new boiler and get a solid bonding point. De-ox the connections well.
It sucks that this isn't nessarally a plumber's problem but could very well be the plumber's problem to prove.
If grounding the unit corrects the issue I'd recommend, in writing, for the school to have a electrical contractor do some forensics work and locate the source of the problem or atleast have both boilers grounded with a cad weld grounding system so it can never be removed.
It is a kids swimming pool with a potential unknown electrical problem.
But that's just my two cents worth, what'da I know, I'm not even a electrician...
