boiler vs steam boiler

boiler and steam boiler both are nouns.

Word	Noun	Adjective	Verb	Adverb
boiler	Yes	No	No	No
steam boiler	Yes	No	No	No

As nouns, boiler and steam boiler are synonyms defined as:

boiler and steam boiler: sealed vessel where water is converted to steam

boiler (noun)	steam boiler (noun)
sealed vessel where water is converted to steam	sealed vessel where water is converted to steam
a metal pot for stewing or boiling; usually has a lid