bbc
The US president called it "very nice" of his Russian counterpart to agree to an energy truce. But details were sparse from the start.
The next day, the Kremlin clarified that Putin's burst of good will expires on Sunday, just as the coldest weather bites.
There is usually a week or more gap between massive aerial attacks in any case, so it's unclear whether Russia has actually paused anything.
There has been no major strike since 24 January, when hundreds of tower blocks in Kyiv lost power and heating.
Ukraine's heating system is breaking down though.
The Geneva Convention, the laws of war, bans attacks on infrastructure that cause excessive harm to civilians.
But this is the fourth winter in a row that the energy grid has been targeted by Russia deliberately, leaving it more fragile and harder to repair after each successive strike.
There were widespread power outages across western and central Ukraine on Saturday after a "technical disruption" affected power lines connecting its grid to those of Romania and Moldova, its government said.
Engineers have been drafted in from Ukraine's national rail company and elsewhere, working around the clock to restore electricity, and to defrost and patch up the heating pipes that run beneath giant apartment blocks in Dnipro, Kyiv and beyond.
An extended pause in strikes on the sector would provide a welcome break, but few Ukrainians trust Russia to deliver that.