Economy 7 - immersion heater help?

Johncore

I've recently moved into an all-electric flat, and this is the first time I've had to deal with an immersion heater, so I don't really know what I'm doing.

My immersion tank is totally unlagged at the moment, which I know is criminal but I'm working on it. It has 2 heaters that go in at the side, one at the bottom and the other about half-way up. They both run to separate on/off switches on the wall, and the guys who installed it said they thought the lower heater would only draw power during E7 hours, and the top will run constantly. They told us to just leave both on all the time, "unless the water gets too hot. "

One thing that's confusing me is that I can't find a single thermostat anywhere in the flat. Should there be one? Will there be one underneath the heater covers? Secondly, the plumber's advice sounds like absolute nonsense. What's the best way to use it, once it's properly insulated?

Also, usage - I finally had my PPM removed last week for a credit meter, and in exactly 7 days we've used 103kWh day and 101kWh night units. 2400 units a quarter seems like a lot, is it? It's a pretty small 2 bed flat, and the only heating we're using is one storage heater at about half input and one 2kWh space heater for a couple of hours in the E7 part of the morning. Turning off the immersion during the day doesn't seem to have made any difference overall.

macman

Completely wrong advice from your plumber. The lower element should be set up on E7 to heat the whole tank at cheap rate, the higher one just heats the top and is basically a boost to top up in peak hours if you run out of hot water. Leaving them both on is expensive and unnecessary.
The sensible way to set this up it to have the main element on a simple timer so that it heats up for a couple of hours during the E7 period (say 5-7am). The other one can be operated manually to boost if necessary.
Or a better option is an E7 programmer like this:
http://www.allaboutelectrics.co.uk/immersion-heater-control.html
If he had just installed this, surely he knows how it works?
And get it lagged immediately-a jacket will cost you a few pounds at any merchant, and save you a fortune.

pinkteapot

I had an all-electric flat for a few years. The plumber is correct that one switch is night-only (cheaper E7 rate) and the other is powered all the time.

Leaving the immersion on 24/7 will be completely unnecessary though unless you take hourly baths.

I used to leave the night switch on permanently (unless going on holiday). It only works during the cheap night-time hours so there is no need to turn it on at night and off again in the morning. It can be switched on during the day but it won't do anything. This heated the water for 7 hours at night and always gave me plenty to see me through the next day.

If you have a bath, you'll use up most of the tank so if you then want some hot water for later the same day you might need to use the day switch for an hour.

There won't be a thermostat - immersions are pretty much an on/off operation.

macman

The thermostat is under the cover at the top of the housing. If there wasn't one, the water in the tank could boil.

Johncore

Great advice both, thanks.

Could I install that programmer myself or would it need a spark? I know what I'm doing and it's not in the bathroom, but I have no idea what the regs are for DIY these days. I know it says "standard size Economy 7 wall-box" but there's nothing that shape in the flat, the heaters are on separate standard light-switch sized boxes.

macman

That unit forms the front panel, you would need an electrician to route the cabling to into an E7 back box.
A simple timer would be the cheapest (though not the best) solution.