The problem with the two that are down to 100l each is that the holiday cottage business has gone mad!
Normally, I'd expect to let around three weeks for the whole of January, February and March, but this year we have been virtually solid for all three months, and it continues all the way to the end of November.
We did have a run of five empty days for one of them, so started to do an 'enhanced' clean. Then the 'phone rang, and a couple wanted to book two nights this weekend. All this means that the heating is on continuously at a time when it's normally switched off.