This is where all the energy is going.
I can't believe that a hot water system is being continuously energised.
45% of a house's power consumption is through an Immersion heater, more if it is old, just to keep the thing warm in the colder months.
Mind you, we are talking about Auckland here, the place that never gets below 10C
Like you say, Craig, you have teenage daughters, now that has to waste your hot water!
What size is your cylinder?, as it sounds like it might lack capacity.
BTW, if you run your cylinder with a timer on it, my lights down here might be a bit brighter!
