A smart meter reading every half hour, a consumer unit with six ways in it, and a clamp on every one of them. The six add up to nineteen watts. The meter says four hundred and eleven.
I own one flat and I let it out, and I am an electrician, which is the only reason this story has numbers in it.
The flat is a one bedroom conversion on the first floor of a Victorian terrace, and it was rewired in 2017 by me, to the current edition, and signed off and certified, and I know every cable in it because I pulled every cable in it.
The consumer unit has six ways. Lights, sockets, kitchen ring, immersion, shower, and a spare that is blanked off and has nothing behind it.
It is let on six month tenancies and there are gaps. Four weeks in 2021, six in 2022, eleven last year when I was doing the bathroom.
During those gaps the flat is empty, the fridge is off and propped open, the immersion is off at the isolator, and everything is unplugged, because I am the sort of person who unplugs things.
Standing load in that state should be the smoke alarms, which are mains with battery backup, and the doorbell transformer. Nineteen watts, which I have measured with a clamp meter on the incoming tails and which is exactly what you would expect.
The smart meter says the flat uses about four hundred and eleven watts, every night, from a few minutes after midnight until about twenty past four.
Let me put that in money, because that is how I noticed.
Four hundred watts for four hours is one and a half kilowatt hours. Call it forty pence a night at the rates when I first saw it, and twelve pounds a month, on an empty flat.
I saw it in 2021 on the supplier's app, which shows half hourly consumption as a bar chart, and I assumed a billing error or somebody's estimate, and I rang them, and they told me what every supplier tells you, which is that smart meter half hourly data is read from the meter and is not estimated.
So I got the meter checked. That is a process: you ask for an accuracy test, and if the meter is found accurate you pay for the test, and if it is found faulty they do not charge you.
It was found accurate. I paid eighty four pounds.
What I did then is what any electrician would do, which is find the circuit.
I put a clamp on each of the six ways in the unit and logged all six for a fortnight, with the flat empty. I had the loggers from work and nobody minded.
Lights: nothing. Sockets: the alarms and the bell, nineteen watts, flat. Kitchen ring: nothing. Immersion: nothing, isolated. Shower: nothing. Spare: nothing, it is blanked.
The incoming tails, clamped above the unit: nineteen watts.
The meter, over the same fortnight: four hundred and eleven watts for four hours a night, every night.
Everything downstream of the meter adds up to nineteen. The meter is measuring four hundred and eleven. Those two statements cannot both be true unless something is drawing current between the meter and my consumer unit, and the run between them is a metre and a half of eight millimetre tails in a plastic trunking that I fitted and that I have had the lid off eleven times.
The things people suggest, all of which I have done.
The neighbours are on my supply. This is the serious one in a Victorian conversion, where somebody in 1974 did something nobody recorded. It is also checkable: I had the supply cut off at the cutout by the distribution company in 2022, for two hours, on a weekday, with notice, because I told them I suspected an unauthorised connection, which is a thing they will always come out for.
With my supply dead, the flat below and the flat above both had power. I stood in both of them with the lights on.
And my meter, during those two hours, recorded nothing. It was dead with everything else. The bars on the app are empty for that afternoon.
It is not somebody borrowing my supply, because if it were, their lights would have gone out.
A faulty meter. Tested, certified, and then replaced anyway in 2023 when the supplier upgraded the estate to a newer model. The new meter reports four hundred and eleven watts between about ten past midnight and about twenty past four.
Different meter. Same number.
The number is what I keep coming back to.
It is not exactly four hundred and eleven. Across four years of half hourly data the nightly figure sits between three hundred and ninety six and four hundred and twenty two, and the half hours within a night vary a little, the way a real load does when a thermostat cycles.
Four hundred watts with a slight cycle to it is a very specific thing. It is not a heater, which would be two or three kilowatts. It is not a fridge, which is a hundred and fifty and cycles hard. It is not lighting, which does not cycle at all.
Four hundred watts, cycling gently, for four hours, is an immersion heater on a thermostat in a well insulated tank, or something very like one.
My immersion is three kilowatts and it is isolated and I have clamped it.
The last thing, which is the reason I have written this instead of just paying it.
The flat has no tank. The hot water is a combi boiler on the kitchen wall, fitted in 2017 when I did the rewire, and before that it was an electric shower and an immersion in a cylinder in a cupboard off the hall.
I took that cylinder out myself. I remember it because it was a pig to get down the stairs and I did it on my own on a Sunday.
The cupboard is a cupboard now, with the hoover in it. There is a capped pipe in the floor and a blanked junction box on the wall where the immersion's supply came from, and the cable back to the unit was pulled out, because I do not leave dead cable in a wall.
In the February I sat on the floor of that hall from half eleven at night until half past four with a thermal camera from work, which is a nine hundred pound camera and which I had signed out properly, pointed at the cupboard door.
At about ten past midnight the door panel started to warm up, from the bottom, in a shape. By one in the morning the middle of that shape was eleven degrees above the wall either side of it, and the shape was a cylinder, about four feet tall, with a band round it a third of the way up.
I did not open the door, and I have thought about why and the honest answer is that the hoover is in there.