Aga questions
Has it been shown that it was in use at the time? Even at the warmest time of the year in the UK.
Was it a coal Aga or another fuel?
It's assumed the Age was on. However, the Bambers' had alternative means of cooking, and it would be reasonable to think they had alternative ways of heating water. Such being so, there'd have been no need to be running the Aga 24 hours a day in the height of summer...........or even at all during summer months. There wasn't likely to be gas laid on. It was an old model so unlikely to have been converted to electric, ergo, there only remains coal or wood.