I am not sensitive about having a degree as I have a Master's degree and have been a vocational teacher for over 35 years. That means I am licensed to teach the trade that I am licensed to do.
I would not call a medical doctor to fix my gas heater, nor a lawyer to fix my plumbing. There are pros in each area that know what they are doing.
As said previously, the manufacturer recommends in the instructions for both the heating equipment and the new parts that a licensed, experienced tech do the repairs to retain warranty and safety. It is necessary to argue with the manufacturer to get him to change his mind. The techs will follow and recommend their instructions, perhaps not the DIY.