saucepan vs water boiler

saucepan

noun
  • A deep cooking vessel with a handle and sometimes a lid; used for boiling, stewing and making sauces. 

verb
  • To cook in a saucepan 

water boiler

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

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