My neighbour regularly goes to NZ for a month in January. Shortly after she'd left a couple of years ago I noticed that her boiler wasn't blowing clouds of condensation out across to my back door as it usually does.
Rang her son and told him his mum's boiler wasn't running and a cold spell was forecast. Instead of coming to check the problem he rang her and reported back that she definitely remembered setting the thermostat to 15ºC. A few freezing days later the house was obviously very wet… phoned the lad again. This time he came over… discovered his mum had indeed set the 'stat 15º, but had absent-mindedly switched the boiler off too.
It was 8 months before she could move back in.
If you've someone you can trust to check the place if there's a cold snap, I'd give them a spare key.