boiler vs water boiler

boiler

noun
  • An apparatus for heating circulating water or other heat transferring liquid. 

  • An old woman. 

  • A device consisting of a heat source and a tank for storing hot water, typically for space heating, domestic hot water etc., disregarding the source of heat. 

  • A sunken reef, especially a coral reef, on which the sea breaks heavily. 

  • A person who boils something. 

  • A steam boiler. 

  • Boilerplate. 

  • A tough old chicken only suitable for cooking by boiling. 

  • A kitchen vessel for steaming, boiling or heating food. 

water boiler

noun
  • An electric device which heats water up to boiling temperature. 

How often have the words boiler and water boiler occurred in a corpus of books? (source: Google Ngram Viewer )