Yes, one month...
We had been billed for 4 months but the previous owner never notified them so they did a breakdown and we got hit for 140!! I will see how our next bill is then I will query it I suppose.
We do use the hot water a lot so maybe that uses up a lot.
You say set the heater input at 6 and the output at 1. How long does the heat store this way for?? And what time does the storage heat come on??? I think its 12am, is it??