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Immersion heater - economy 7 timer wiring
Tom Luknar
14 Posts
Question
Hello,

I have a honeywell st6400c controller and an immersion heater. 
My heater has 2 switches, off and on peak. My concern is that the heating works only with both switches on. Even if its set to trigger at off peak time only, which it does, both switches light up and if I switch off the onpeak one, the heating stops even tho the offpeak is still lit (testing this at off peak hours ofc). Is this correct ? does this not use much more electricity? I was monitoring this and Im sure it goes against the "night" hours, but my worry is that it uses much more power than it should.
Thank you for your advice
Tom
46 Replies
mapj1
2170 Posts
Difficult to be sure without seeing how it is wired, but do you have 2 elements in the tank (one high for just heating half a tank, one low for heating a whole tank) or one element and a change over switch?
I'm also assuming you have 2 sets of cables from your meter, some that are live all the time and some that are live only at off-peak times.
Please check this is true before reading the below, as it may not be the case.

The 6400 is normally used with hot water and heating,  and is in effect a pair of time clocks, that operate two groups 
of  contacts that can keep different times.  manual can be downloaded here 
As such this is not normally used with E7. Equally you could have the two clocks wired with one on each supply, or there may be a change over relay somewhere so that whenever the E7 supply is on, the system uses it, but if there is demand at other times, then it gets put on the day rate supply.
Basically to be able to help we will need you to do a bit of detective work.
AJJewsbury
1677 Posts
I think most E7 systems charge everything at the off-peak rate overnight - so an off-peak supply can sometimes be emulated by using a single 24-hour circuit and a time switch that only switches on during the overnight period. That saves running an extra cable and so on, but has the disadvantage that if your clock and the supplier's get out of sync you can inadvertently end up using electricity at the peak rate instead - or indeed get into a right tangle if the user doesn't understand exactly what's going on and tries to re-program their clock.
   - Andy.
Sparkingchip
2675 Posts
You say “an immersion heater” so presumably just one immersion heater, therefore the two switches are linked together after the switches, therefore both lights come on.

Set the clock and leave the peak switch off so it runs through the clock.

Andy B.
Sparkingchip
2675 Posts
Check the time the suppliers meter is set to and set the immersion clock to match if the time is out.

Andy B.
Typiod
59 Posts
If the clock is in fact an ST6400c then it only has 3 amp switching contacts.
Sparkingchip
2675 Posts
Typiod:
If the clock is in fact an ST6400c then it only has 3 amp switching contacts.


I had not spotted that it is not even an immersion heater timer, throw it away as if it has been run controlling an immersion heater as it is scrap.

If it is not actually controlling the immersion heater and is in fact controlling a central heating boiler it could be a gravity system and the heating won't run without the hot water.

Andy B.

Sparkingchip
2675 Posts
Unless the immersion heater is controlled through a relay, which I really doubt.
Tom Luknar
14 Posts
Hi guys,

thank you all very much for your response, although half of it doesn't mean much to me as I'm, well, without any knowledge on this topic.
I'm not even sure now whether it's an immersion heater (as I have emailed honeywell as well and they said they don't use their controllers for immersion heaters, what means im most likely wrong)

I have figured out it's gonna be easier for you if I add some pictures to the topic so you don't waste your  time on me too much.
Please see attached. I now know, they are separately connected to the top and bottom of the tank, which I haven't checked before (apologies). I thought I could read it off the tank what sort of a heater this is but can't figure it out..(the agency nor landlady are not any good which is annoying and weird at the same time). As you can see, the onpeak is wired into the bottom, off peak is wired into the top. As I've mentioned before, the off peak, even tho it gets lit as per timers settings, does nothing if the onpeak is not switched on. (I have tested it tonight) I hope this gives you more insight - i'm definitely learning from your answers. 
I should have mentioned that I have switched electricity supplier recently. (this was finished less than a week ago)
Also, I'm not entirely sure how to set the controller against the timer in the utility room as well, it just rolls . The offpeak hours seem to be running until about 7:15 in the morning what strikes me as a very odd time. 
Thank you
Kind regards
Tom

Tom Luknar
14 Posts
Tom Luknar
14 Posts
Sparkingchip
2675 Posts
How do you heat your rooms?
Typiod
59 Posts
It would appear that there is no output tail from the timeswitch.
Tom Luknar
14 Posts
Heya,

same way as the tank - via the honeywell controller.
the whole electricity in the house is a bit insane to me. 70+ spotlights bulbs all over the place. at least they can be lowered intensity but still. during covid we had not much choice as we couldnt personally visit and inspect the house to the detail. its not bad as we dont need them lit almost nowhere at any time. 

 
Blencathra
76 Posts
Typiod:
It would appear that there is no output tail from the timeswitch.

Whats the thick grey in the middle? most T/S outputs are on the right ,but this looks like a Sangamo and i think they were slightly different

Typiod
59 Posts
Blencathra:
Typiod:
It would appear that there is no output tail from the timeswitch.

Whats the thick grey in the middle? most T/S outputs are on the right ,but this looks like a Sangamo and i think they were slightly different

Not any of the many hundreds of Sangamo timeswitches that I have fitted over the years. The 25mm in the middle will be the nuetral.

mapj1
2170 Posts
Thank you for the pictures they do indeed help.

You have 2 immersion heaters, one at the top for when you pnly need half a tank. and one at the bottom for the whole cylinder.
you may be able to work out by touching the silver cloured caps if both or just one is operating, after about 15mins.

The metering, oh boy. To be sure it would be good to see a bit more at the top of the pic, to verify the connections into that black box at the top (the 'henley block')  and  I assume there is a consumer unit near by with lots of fuses or breakers but here is what I think I see.
You only have one supply to the rest of the building, not two cables one for Off peak one for day rate - this makes things easier.
Shiny new meter (the white bit) and time switch (clock - the black thing ) is state of of the ark.

The clock uses the little thin wire between it and the meter to tell the meter which of the two counters it has is the one to be  used right now. (the thin wire will be at a voltage near live when it is one rate, and near neutral when it is the other.)
(and when the meter is read, there are two numbers one is the running total for day units and the other for night units )
So once the time switch has gone clunk everything in the flat is charged as  cheap rate, until it goes clunk again.

And where is the heating controller, and how do we ensure that  it's times match those of the E7 metering clock ?
 
Sparkingchip
2675 Posts
I would assume the immersion heaters don't need a time clock, the bottom heater is presumably connected to the E7 supply and just comes on at night and should be left turned on at all times as it gives you a tankful of hot water heated on the lower priced E7 tariff, the top one is presumably connected to the 24/7 supply and should only be turned on if you run out of hot water as it costs twice as much to run, therefore you only get half a tank of hot water for the same cost as a tankful using the bottom heater. So leave the top heater turned off unless you run out of hot water and need a boost.

It could be controlled better using a simple push button timer on the top immersion to turn it on for a set time, for example like this so it doesn't get left turned on and as I said the bottom heater probably doesn't need a timer at all.

I cannot imagine what the ST6400c is doing, unless someone has made up a homespun control unit using relays or it is severely overloaded it cannot be controlling the immersion heaters.

Andy B.
Tom Luknar
14 Posts
Hi, 

the st6400c controls everything - hot water and heating. theres no other way to switch either of those on to start the heating process. no other switches or anything. if i dont change the controller to "run programme" and move one of the sliders to once or cont. it wont work.

additionally, if the onpeak switch isnt on, it wont work, no matter the time of the day. same as if i use the honeywell controller to auto trigger the heating in early morning. it needs the onpeak ON.

as far as im aware. the onpeak switch shouldnt be used unless as you said i need to do the heating during the day which i never do. so why is it necessary to be on for the offpeak heating to run is a mystery and reason ive raised this. i believe it worked well when ive moved in and im not sure whether this is caused by the supplier switch or something else has gone wrong as i really dont see the reason why it would make any difference. especially in regards to the controller and switches. 

i do have solar panels too, thought the rest of the boxes are only related to them. although again, no idea how they help me save energy as i think the heater  takes about 0.01kwh every 2 seconds
Tom Luknar
14 Posts
Blencathra
76 Posts
How do you explain the other tails, looks like L/N/switched neutral in 4mm and L in Lout in 16 or 25mm
Typiod:
Blencathra:
Typiod:
It would appear that there is no output tail from the timeswitch.

Whats the thick grey in the middle? most T/S outputs are on the right ,but this looks like a Sangamo and i think they were slightly different

Not any of the many hundreds of Sangamo timeswitches that I have fitted over the years. The 25mm in the middle will be the nuetral.

 

Tom Luknar
14 Posts
Tom Luknar
14 Posts
Typiod
59 Posts
Blencathra:
How do you explain the other tails, looks like L/N/switched neutral in 4mm and L in Lout in 16 or 25mm
Typiod:
Blencathra:
Typiod:
It would appear that there is no output tail from the timeswitch.

Whats the thick grey in the middle? most T/S outputs are on the right ,but this looks like a Sangamo and i think they were slightly different

Not any of the many hundreds of Sangamo timeswitches that I have fitted over the years. The 25mm in the middle will be the nuetral.

 

It would go
Live in (usually 80A rated)
Live in (25A rated, to run the clock)
Neutral in (80Amp) (this has also been linked across  to give a neutral for when the meter switches)
Neutral out
Live out ( but nothing there)

Edit to add I would be getting the meter operator out as the neutral for the proprty is going through the clock snd thus on the smaller cable back to the head.

Typiod
59 Posts
Tom out of intrest what do you have for space heating? Is it radiators, storage heaters or panel heaters.
Blencathra
76 Posts
80amp neutral? are you an ex board man, I was with NORWEB, whats the other neutral for straight out of the cut out?

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