on the boil

Short definition from Wiktionary

Prepositional phrase

1. 1
   simmering strongly and about to boil.
2. 2
   About to happen; imminent.
3. 3
   boiling.
4. 4
   continuing; active; in a state of activity or development.
5. 5
   Going smoothly; working well.
6. 6
   Playing exceptionally well.
7. 7
   (Of a player taking a pass) running at full speed towards the opposition.