Go Off The Boil Meaning

(idiomatic, Britain, Australia) To become less successful.

Example: 1891: The Farmers' Alliance History and Agricultural Digest, Nelson A. Dunning (ed.)
  All puddings must be boiled in plenty of water, turned frequently, kept closely covered, and never allowed to go off the boil.
1972: The Cuisines of Mexico, Diana Kennedy and Craig Claibourne
  That is the reason for the coin. You will be able to hear it dancing about, and it will tell you if the water goes off the boil or is getting dangerously low.
1955: The Big Lie, John Baker White
  As one of the rearguard put it, "We laid up until the Hun had gone off the boil a bit and slipped out the following night."
1987: The Female Form: Women Writers and the Conquest of the Novel, Rosalind Miles
  But John, not surprisingly, has gone off the boil, and feels nothing for Annette so strongly as an intense weariness and desire to be rid of her.
2004: American Gods, Neil Gaiman
  Wednesday to Shadow, "I don't sleep. It's overrated. A bad habit I do my best to avoid - in company, wherever possible, and the young lady may go off the boil if I don't get back to her."
2009: Somewhere Towards the End: A Memoir, Diana Athill
  By then we'd gone off the boil sexually and he was even less keen than I was about 'marriedness', so it was more like friends deciding to share a flat than the setting-up of a ménage.