Can "grew warmer" be used as a replacement for "became warmer" anywhere? I've started to think of the phrase "grew warmer" and it seems kind of strange. Things can become warm, but it sounds strange to say that some things grow warm. Like for an inanimate object that doesn't grow, how is it ok to say that it grows warm? Can someone explain this?
"Grew" is perfectly fine here; it is simply metaphorical.
the kettle was boiling.
is perfectly fine. For the kettle to grow warm is also fine.