Green’s Dictionary of Slang

chill v.1

[abbr. SE take the chill off]

to heat up.

[UK]Dickens ‘A Passage in the Life of Mr. Watkins Tottle’ in Slater Dickens’ Journalism I (1994) 431: A pint pot, the contents of which were ‘chilling’ on the hob.
[UK]Sl. Dict. 116: Chill to warm, as beer. This at first seems like reversing the order of things, but it is only a contraction of ‘take the chill off.’.