Immersion heater - elements wired the wrong way around?

[st07]

Hi.

My mum recently moved in to a flat which has Economy7 and an immersion heater installed. I remember reading somewhere that the bottom element of the heater is for Economy7 heating during the night, and the top element is for 'boost' heating.

Today I noticed that the neon light on the wall plate for the bottom element was lit. The wall plate for the top element was extinguished. It appears that the top element is being fed from Eco7, and the bottom is 'boost'.

I have rewired them back round to how I think it should be. Can someone confirm this is correct?

Many thanks

 

[RF Lighting]

Yep.

Heat rises (basic physics)

So if you use the top element it will only heat the top of the cylinder. This takes less electric than heating the whole cylinder, so would be used as a boost using full rate electric.

The bottom element heats the entire cylinder, starting from the top down. One the water surrounding the element is hot enough for the element to click off the whole cylinder needs to be hot.
This takes much more electric than just heating the top bit, so you would want to use cheap electric for this.

 

[st07]

Excellent, thank you for your prompt reply. How strange that it wasn't wired correctly before.. Never mind.

For reference, here is a picture of the heater:

One thing I noticed when I took the metal cover off of the thermostat, was that the thermostat has no 'degree' markings but rather just simple notches with + / - on either end of the scale. This gives little indication of what the temperature setting is. Also, I read somewhere on here that pre-2004 thermostats do not have a 'reset' button and indeed the thermo for this heater has no 'reset'.

I'm planning on replacing the thermostats, but am unsure on the element size. Is there any marking or indication on the cylinder itself that would save me from taking out the element and physically measuring it?

Many thanks again

 

[Taylortwocities]

Why do you need to remove the whole element? The thermostat will pull out from the middle of the element housing after you have disconnected the wires.

You can buy replacment stats with cut-out built in to them. Like these:
STAT

 

[st07]

I assumed that I would need to know the element size to be able to purchase the correct size thermostat.

In saying that, I think the thermo is 7", certainly not 11" which is the next size up. Looking at the pictures given on that website, the normal thermo looks identical to what I have. Am I wrong to have thought that thermostats without 'safety cut out' were illegal then?

 

[Taylortwocities]

Look on that site for immersion heater thermostats, they have several sizes. I just picked one as a sample.

Just pull out your old stat and measure it, get one the same length.

Its better to put in one with safety cut out (only about £3 more) because it stops your tank fillign with boiling water if the stat gets stuck on. This has caused death and severe injuries to folk in the past. .HOT!

Some have a separate cut out screwed to the body of the immersion housing & some (like the one in the link) have it built in.

From April 2004, new and replacement Immersion Heater Thermostats need to incorporate an overheat safety cut-out

 

[st07]

Good point. The live feed goes from thermostat, in series to something else, then to the element tag. Perhaps the 'something else' is a thermo that cuts out at high temperatures?

My next set of questions:

What's the best temperature to set the Eco7 thermostat at?
How long on average would it take to fully heat a 120 litre immersion tank (3KW element, Eco7 rates)?
Would it be worth investing in an immersion heater timer to keep costs down?
When is the best time / when is it most suitable to use the 'boost' element?

Sorry for all of the questions, and thanks very much in advance for your replies

 

[Steve]

HOUSEHOLDERS in Swansea are being urged to check their immersion heaters following a baby's death.

Why? Is the problem restricted to Swansea and Somerset? Do no other towns in the UK have similar installations? [/sarcasm]

 

[Taylortwocities]

The live feed goes from thermostat, in series to something else, then to the element tag. Perhaps the 'something else' is a thermo that cuts out at high temperatures

Yes that the cut out. So just get a standard stat if u replacing, you dont need another cut out.

Re timing. have a look at one of these. made for the job
http://www.tlc-direct.co.uk/Products/HOELEC7.html

 

[kai]

It appears there is no earth bonding in the immersion heater cupboard?

 

[RF Lighting]

Why would there be?

 

[kai]

Immersion cupboards tend to be next to bathrooms - it's often more convenient to do the supplementary bonding in the cupboard adjacent the bathroom - the install looks like it predates the 17th - surprised at the lack of earth bonding - especially if the immersion is non-rcd protected.

 

[st07]

What is supposed to be earthed to where in my picture? AFAIK the fuse box has MCBs with a big RCD feeding the lot, if that makes sense.

 

[Spark123]

Not so much earthed - under the 16th edition regs there was a requirement to carry out supplementary equipotential bonding for a bathroom, this could be done local i.e. in a cupboard adjacent to the bathroom.
Under the 17th edition regs the supplementary bonding for a bathroom can be omitted if certain criteria are met: //www.diynot.com/wiki/electrics:supbond17th
It might be that supp bonding has been carried out elsewhere.

 

[st07]

The bathroom is opposite the cupboard where the immersion heater is situated.