People would call a plumber to fix a central heating system - but is much of their formal training allocated to things like Boiler Logic, Heat calculations, Flow rates, etc.
After lending an ear to a couple of pal's woes - I wonder if they even knew how a heating system works.
I was perhaps fortunate in having a potty mouthed fitter who had been trained and approved by a boiler firm - and evidenced by him uploading data to register the job for the warranty. I was impressed also by his calculations for gas flow taking into acount pipe lengths and bends.