steam boiler vs boiler

steam boiler and boiler both are nouns.

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

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

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

steam boiler (noun)	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