Noticed my ICOS24 boiler was dripping from the rear right area of the lower plate a few days ago. Isolated the power and called British Gas in to take a look.
The engineer found the issue, a corroded plastic nut that holds the condensate drain rubber hose to the S-trap.
I was amazed as to why...
In the three properties i have lived in over the last 20 years all have had outside taps on the rear wall and i have never bothered to turn off water or insulate them over the winter. They have never caused me an issue (yet)
As you say, UV not an issue when it’s all buried in floorboards.
I hear similar comments regarding speedfit/etc fittings for central heating. Used for 15ish years in all three of my houses I’ve owned and never had a problem.