HVAC is my weak subject. Want to know when inspecting a boiler, what should be done? Can they be opened like a furnace?

HVAC is my weak area also;-) but I can try to help you. What kind of boilers are most common in your area. BTW ya should update your profile so we know what part of the country you are located.

Boilers are a different animal from a gas furnace. Some are hot water only some are steam. Burners are not totally visible on some boiler and visible on others. My big concern would be are the safety’s installed such as relief valves, temp and water level controls, expansion tanks with sight glasses, flame safety cutoffs.
The kind of burner ignition such as standing pilot or electronic. I check for water and gas leaks small or big makes no difference a leak is a leak

Water boilers are most common in my area which is Maryland. Thanks for the reply, it was helpful. All update my profile as well