From Longman Dictionary of Contemporary Englishgo off the boilgo off the boilBritish EnglishWORSE to become less good at something that you are usually very good at He’s gone off the boil after a tournament win in Dubai. → boil
Examples from the Corpus
go off the boil• I knew as soon as I wrote it down I'd go off the boil.• Even extortion has gone off the boil.• Now it appears to have gone off the boil.• We're letting the kettle go off the boil.• The second series really went off the boil because there was much more emphasis on the woman lawyer. 