You Have Also....
....Done your parents a huge favor.
Very few elderly people have any idea what a "control board" is or what it does, much less why it costs $300 plus installation to replace some of them.
One of the tough things about getting older and trying to remain independent is that a lot of things start happening you don't really understand, because it's not your generation any more. You have to start dealing with things on faith that you're not being taken advantage of. It's a little nerve-wracking, to say the least.
This keeps your folks using technology they understand, which should help them feel a little more in control of their lives.
My dad is having these issues - when I was a kid, he single-handedly rebuilt the engine of his 1956 Chevy, because he understood cars of that era. Today, he'll get a "Check Engine" light or an error code and it drives him nuts, because the only thing he can do about it is to take the car in and let the dealer relieve him of some of his hard-won savings.