Many have removable filters that you're supposed to clean periodically. If there's nothing obviously removable in yours then it might have a "self-cleaning" system that would be harder to take out and clean yourself.
Wait until I tell you about your water heater's sacrificial anode. NOBODY replaces those.
I got an electric one so I never need to remember to replace mine!
I think the electric ones need to be replaced eventually too, not not nearly as often.
Yeah I think it's something like a 20+ year lifespan, I doubt I'll even be living in the same house in 20 years.