The basics depend on what system you have.
Ours is a Zavoli multipoint and our service consists of changing the LPG filters in the gas lines to the valve block, that's about it.
Every year or so we get the installer to check it over and update the software, but so far only once in 5 years of running.
Other than that, tanks probably need removing, inspecting and repainting if their 10 years is up.
Peter