How to setup hotwater for off peak only?

[Crabs999]

Hi,

I've recently moved into a new all electric flat and am unsure how to correctly operate the hot water system to have it heat during off peak times.

The tank has two heating elements, that are both connected to a socket in the wall and also to a control box (BX2000) with individual cables.

So far I have tried having the lower element switched on at the wall and then flicking the "off-peak" switch on the control box, but I think the tank is heating all day. I cant see any noticeable energy usage on our smart meter during the night, and there are spikes in energy use after we shower.

There is also an additional panel of indicator lights on a nearby wall. It seems that the left light is for the lower element and the right light is for the upper element. If either of the elements are turned on at the wall, the corresponding light comes on, regardless of the time of day.

My question is how do i set this all up so that the tank only heats during the night? Should I have the elements switched on at the wall and the control box, or just one?

 

[Madrab]

All depends on how the system is wired, what kind of meter you have and what kind of tariff you're on. Is this a rental property?

That type of controller used to have 2 connections supplied by a consumer unit and a meter that switches between peak and off peak through those 2 different sets of cables. The off peak cables would only become energised during off peak, and that would typically run electric storage heaters and the HW off peak side of things. If they aren't present then the system will just run on the normal supply and only at certain times of the day would off peak become relative but they would run all the time.

If it's rented then time to talk to the landlord, if not then time to talk to an electrician or your supplier.

 

[Crabs999]

Yes we are in a rental property, I have asked the landlord these questions but they have not been very helpful, I might need to insist on having an electrician come out.

We are with Octopus energy with an economy 7 tariff. We have a smart meter but I am not sure of the specifics.

My major confusion at the moment is why the two immersion elements are connected to both the control box and a socket? If I want the power to come from the control box, should I then have the socket connects for the elements turned off? If they are on will this override the control box?

 

[JohnD]

connected to both the control box and a socket

I have looked carefully at your pictures and I cannot see a socket.

What do you mean when you use the word "socket?"

 

[Crabs999]

Apologies, I am Australian and im not sure what the most accurate terms are. I am talking about picture 2 with the switches controlling power to the elements.

From each element, one cable feeds into these switches, and then the other goes to the control box. You can see the two cables most clearly in picutre 3.

 

[JohnD]

Those are switches.

 

[JohnD]

FYI (No offence intended) this is the uniquely wonderful UK fused and shielded plug

And thus is the wonderful shuttered and earthed socket it fits into

 

[JohnD]

From each element, one cable feeds into these switches, and then the other goes to the control box.

Rather strangely, the elements seem to have been given a supply from the control box (which is correct) and, unaccountably, an addition parallel supply via switches. The switches might be intended to manually provide power outside the off-peak period, but the timer can do that.

It is concerning that the switches can backfeed power down the other wires into the controller and the off-peak circuit, possibly making it live when it is supposed to be off,

 

[Murdochcat]

How is the property heated? It looks to me that the lower immersion is not controlled by economy 7

 

[Crabs999]

Rather strangely, the elements seem to have been given a supply from the control box (which is correct) and, unaccountably, an addition parallel supply via switches. The switches might be intended to manually provide power outside the off-peak period, but the timer can do that.

It is concerning that the switches can backfeed power down the other wires into the controller and the off-peak circuit, possibly making it live when it is supposed to be off,

So in theory I should have the switches turned off and just use the control box?

 

[Crabs999]

How is the property heated? It looks to me that the lower immersion is not controlled by economy 7

We have two electric heaters. There is no gas in the flat. I agree I don't think the switch for the lower immersion is economy 7, so I think we need to use the control box?

 

[stem]

The usual way would be to have the bottom element wired to a separate off-peak consumer unit* (a box containing circuit breakers) that is in turn connected to the electric meter in such a way that it is only energised when the 'off peak' tariff is available and therefore whole cylinder of hot water is heated every time the cheaper electricity is available.

When the off peak rate is available for use this light should be lit.

The 'Off-Peak Supply' switch on the Horstmann is normally left permanently on, so that whenever cheaper electricity is available the water is heated. This is connected to the bottom heating element to maximise the amount of water heated during the cheaper rate.

The Horstmann box would also operate the top element using the 'normal supply' and can be used to manually boost the hot water if you needed a top up during the day when the cheaper rate isn't available. Pushing the 1 hour, or 2 hour buttons switch the top element on for that period of time.

The two switches just above the skirting board in your second picture are used for isolation during maintenance and are normally left permanently 'on' with all control being carried out at the BX2000

This is a standard method of installation, but this assumes it has been installed properly, so you may need to have a professional examine and test the system to determine how it is actually connected.

*where an separate off peak consumer unit (sometime also used in conjunction with electric storage heating) is not available which is not uncommon, an additional timer is usually fitted to switch the supply to the off peak section of the BX2000 and it is set so to only be 'on' when the off-peak supply is available.

 

[Crabs999]

The two switches just above the skirting board in your second picture are used for isolation during maintenance and are normally left permanently 'on' with all control being carried out at the BX2000

If they are 'on', is that not going to override the BX2000? Should they not be off?

 

[Crabs999]

When the off peak rate is available for use this light should be lit.

View attachment 395782

I have noticed that if I flick the 'normal supply' and 'off-peak supply' switches on the BX2000 to the on positions, this light comes on and stays indefinitely. The boost buttons also do not do anything. I cannot recall what happens if only the 'off-peak supply' is turned on.

 

[ericmark]

These are switched fuse connection units. (FCU) I would think they both need to be on. And the timer selects which runs. However, the twin cables out of each immersion heater is not normal, so really I would need to test.

I would use something like this

the one I use is more expensive but it does the same thing.

But first, let me explain how water heating works.
Bottom immersion gives you enough water for a bath.
Top immersion gives you enough water for use in a sink.

So I only need the top one, as I never have baths, and my shower does not use stored water.

However, the water in the top will not stay hot for that long, maybe a day, where if the whole cylinder heated, it will likely last 3 days.

So common only to use the bottom immersion heater, which is only powered using off-peak. And for that to last all day. Should the off-peak water run out, then the top immersion is used, to get hot water until the next off-peak starts. If the top one's thermostat is set lower than the bottom one's thermostat, then the top one will auto turn off anyway.

With a single 27" immersion heater, it uses 35 kWh for 28 days. So at 30.17p/kWh = £10.60 and at 8.5p/kWh = £3 so not a massive loss if you end up using peak instead of off-peak.