Boiler furnace inspection

Can you all guide me O’bewon! I am wondering to what level do you guys go when inspection a boiler furnace.
Do you just test it buy turning it on and checking the zones?
Do you manually test each valve?
Do you test the expansion tank?
I am not sure i do everything and am not sure i need to do more but i would like to know all the steps. if you go above and beyound, tell me.
Thanks for any and all imput!
Andy B