The only advice I have is think of it as an appliance. They aren’t super serviceable and are so cheap now that the smart money is on making the whole setup easy to change out like you would with any other appliance.
I constantly see new open box ones on fb marketplace so I’d look there.
Don't use Triangle Tube. I have a combi unit in my shop house for domestic and hydronic heat. Its been a great unit, but they are out of business now, so you cant get parts or warranty. A plumber friend of mine said the supply houses have been liquidating them and not telling buyers.