Getting off Economy 7

Robin9

This has to be more than an immersion running constantly
In theory a 3kw immersion at night for 8 hours would consume some 8760 kWh - (the consumer is actually using about 6000). During the day 17520 kWh (the consumer is actually using about 10000 and id doing all the other things in life like cooking)

Thats theoretical - it practise with a failed thermostat the hot water would be boiling away and would be far too hot to shower or put your hands in.  In practise you would get a tank of hot water in perhaps 2/3 hours - about 3000 kWh. The question remains where is the rest of this consumption coming from.
Unless she has already done so I suggest she reads her meters late tonight, switches off the immersion heater and reads them again at breakfast. She should have a tank of coldish  water

Madmel

Dawn you are using more electricity than we are and I'm paying for a 4 bed house (oil heated) and a 3-bed cottage heated by storage heaters,  Water in the cottage is on a time-switch for off-peak rate.  We also have no gas here.  Altogether, we use 19640 kWh per year (sums done yesterday) and of that, 67.5% is off peak rate.  Where possible, we use the showers & washing machines when it is cheap.  We run dehumidifiers at night too but don't have a tumble drier.  I do have 2 shower-loving adult daughters here.  I was paying £270 per month with Ovo but we are 3 months in credit so I cut down how much we pay.  Due to them making fundamental changes to our contract, we are leaving them, probably for Yorkshire Energy although Symbio appear to be the cheapest.

Follow the advice above about writing down your readings.  Then turn off the immersion heater.  We write our readings down every month and have kept this record since around 2008.  It's now 2nd nature.