Economy 7 and the amount of hot water

nimbus2000

Hi everyone, not sure whether to post this under elect or water........

I think that this might be a stupid question but here goes......

I have an immersion water heater and two days ago I switched to economy 7. The last 2 nights I have been heating the water off peak and the hot water runs out really quickly. Obviously I know that there will be a limited supply, but today I did one lot of washing up and one load in the washing machine in the morning and then when I went for a shower in the evening it was cold. Is that just because the water heated at night goes cold over time (and so I should do a peak boost in the evening) or does it sound like a problem with the heater (it worked fine when it was on peak and the meter is registering about 10 kwh off-peak at the moment).

Oh, and I live in a 2 bed flat with one other person (who is away at the mo so hasnt used any more hot water than i said above) if that helps.

Thanks alot

Magentasue

The water, once heated, should last. Usually, with E7, the immersion comes on overnight - are you sure yours does? How long for?

Fire_Fox

Once you have used some hot water, the tank will refill with cold water leaving the remaining water tepid by evening. Do you usually shower first after you used the immersion, then do washing up/ laundry later? Now you have E7 it's cheaper to put a timer plug on your washing machine and run during the early part of the night, setting the immersion to come on during the later part of the night.Then you will have lots of hot water left for your showers.

Cardew

Sounds like the tank isn't heating at night - stay up late and check if the E7 meter is registering when the immersion is on.

10 kWh is not much as you will use some for 'normal' use during the 7 hours - fridge/freezer, lights etc.

Are you sure that your washing machine is Hot fill? most machines these days are cold fill.

A full tank if insulated will last for far more than you stated.

nimbus2000

I have an off-peak and a peak switch by the heater.....I only have the off-peak switch on at the moment and it lights up at 11.30, im not sure what time the light goes off because its off when i get up in the morning. I was thinking of just switching off the heater altogether 2nite to see how much elec i use during the night without it.... because if its still about 10kwk then its can't actually be working

Premier_2

It could be that by coincidence the immersion heater has suddenly failed, but it sounds like you are getting some heating up of the water, but not enough, so I'm not convinced that's the case.

Could it be that the immersion heaters have been incorrectly wired and when the off peak is coming on, it's only heating a small amount of water, usually what the peak heater should do?

Let me try and explain. Your hot water tank will either have 2 separate side entry immersion heaters fitted, or a top entry immersion heater.

If you have side entry ones, the lower one should be the off peak heater and the upper one the peak heater. Only water above the heater will actually heat up. If this is the case, can you see where the cables go from the switch? Sometimes it's easy to see which immersion heater is controlled by which switch.

If you have a top entry heater it's more complicated. The top entry meter will actually usually be two heaters, although they are both housed under a single boss. There will be a long heater that goes all the way down to the bottom of the tank (inside, so you can't see it) and a shorter one. The long one will heat the whole tank of water and should be the one that runs off-peak, whilst the shorter one will only heat the top portion of the tank and should be used for peak hours boosting. It's more difficult to tell these apart unless you know what you're looking at.

One way to see if they have been incorrectly wired (and this could also be used for the side entry heaters) would be to turn off the off-peak switch, manually turn on the peak switch at 11:30pm when the off peak appears to come on, and manually remember to turn it off again 7 hours later - the timing is not too important, just trying to save you paying peak electricity, but you must remember to turn it off before using any hot water else it'll heat it up again.

If the next day you seem to have plenty of hot water, then the heaters are corrected the wrong way round.

david29dpo

Totally agree and an excellent explanation. I had this on a new build! Sparky must have been pi**ed at the time.

nimbus2000

Thanks for the suggestion Premier. I left the peak switch on last night and will see if i have any more hot water than last time. It did use about the same amount of kwh tho at night as the off-peak switch.

The "peak" cord goes into the heater just under half way down and the "off-peak" cord goes in right at the bottom.

Im in a new build too, so it wouldnt surprise me if they did mess up the installation.

Oh, and I do have a cold fill washing machine, so that wouldnt have used any hot water.

Thanks everyone

Premier_2

nimbus2000 wrote: »

...The "peak" cord goes into the heater just under half way down and the "off-peak" cord goes in right at the bottom....

Oh well, it appears they are correctly wired up ... but was worth checking just in case.