Economy7 Hot water tank on during day

Timfulton

I've moved into a new flat which has an economy7 water tank heater and a day/night rate between 00:30 and 07:30GMT for night and the rest day. My hot water tank seems to be running during the day when only the "off peak" switch is turned on. I keep the boost switch turned off all the time

Is this the correct set up and if so, why does the hot water heat during the day which I assume uses peak energy prices? Does this require an electrician to come and sort out?

Mr.Generous

usually a timer for economy 7 by the meter - simple check, is the clock right?

Timfulton

Yes the clock seems to be right - it is running on GMT but I understand this is normal for older systems to remain on GMT all year.

CashStrapped

There are a myriad of ways E7 circuits are set up.

Some items such as storage heaters and off peak immersions may only get power supplied to them during off peak. So they are on a time specific circuit.

However...

It is possible, dependant on how the circuit is set up, that the off peak immersion is not cut off when off peak period ends. The power supplied may just start using peak energy. So it is not on a time specific circuit.

It is only considered an off peak immersion because it is usually the larger of the two, which is designed to heat the whole tank. The boost (peak) immersion is usually smaller.

So, if you just have a simple on/off switch for the off peak immersion. As soon as the tank cools during the day, the off peak immersion thermostat will detect this and turn on to heat it up again. During the day, this will obviously use the peak rate.

A way round this is to replace the immersion on/off switch with either a simple (mechanical) timer or a digital one. This will allow you to specifically set when the off peak immersion is allowed to come on.

A way to test what is happening is to turn everything off during the day. The tank should be cold/luke warm when you do this. Then turn the "off peak" immersion on at the switch. If you see the peak meter reading whizzing round, then you know that the "off peak" immersion is not on a time specific circuit and can use electricity at any time of day and at any rate.