Hello Russell,
Thanks for your enquiry and your photos, you’re correct in thinking this is due to the sun, although this is very severe UV damage; is there a conservatory or big glazed patio doors nearby that reflect and concentrate the sun’s rays.
From the fitting date clock I can see it was manufactured in November 2011 so coming up 7 years old. UV damage is initially a surface cosmetic effect and if you lightly scrape the surface with a sharp blade you will find the discolouration is very thin.
Over many years in this sort of exposure, probably 20 to 30 years, the material surface will start to craze and become brittle but structurally the fitting will still function. To improve the aesthetics of the pipework you could paint it, a gloss white or black, and this will also give it some UV protection.
I hope our comments are of some help and thanks again for your enquiry