Dual Meter / Horstman E7BX query

[Callum M]

Hi there.

I’m looking at removing my existing SINGLE 3kW immersion heater /cylinder and replacing it with an Ariston Europrisma unvented water heater as my bills are through the roof and the flat is unoccupied a lot of the time and when it is occupied demand is very low as the large cylinder only feeds 2 hand basins (shower is electric).

I currently have 2 meters (Low and Normal) and I believe I’m on an Economy 7 tarrif with an old Horstman E7BX controller which I assume is wired to the Immersion heater (I have no Storage Heaters). My understanding of this controller is that it works by automatically completing the circuit as soon as electricity comes through the “Low Meter” during non-peak hours, as such the ring that the immersion heater is installed on automatically comes on to heat the water at cheap rate.

Furthermore, when I turn the “2 hour boost dial”, when I need a boost (which is never), presumably this completes the circuit from the day meter which then energises the ring main that the heater is installed on? Does that sound vaguely correct?
I can’t see any other way that the immersion heater would “know” to come on after hours as there are no other clocks or timers or anything.

My question is this:

If I were to plug in the new Ariston heater into the same socket as the existing Immersion heater is run off (both are 3kW, 13A), presumably this would only come on by default at night time, and if I needed a boost during the day, I would have to turn the dial. If this is the case, I’m concerned that due to the new system only having a small 15 litre tank, I will run out of hot water during the day unless I kept “boosting” it. Does this sound like a valid concern?

If I was to switch the Horstman controller “off”, would this solve my issue and enable the heater come on regardless of the time of day?

A couple of photos are below, I have no idea what the switch on the left of my fusebox is for. I turned it off and it didn’t seem to change anything, so I left it off. Any ideas?


Many thanks for looking, and any advice you can give a keen

amateur

 

[stillp]

Get rid of the E7 tariff! It's costing you a bomb.

 

[JohnD]

Hi there.

I’m looking at removing my existing SINGLE 3kW immersion heater /cylinder...as my bills are through the roof and the flat is unoccupied a lot of the time and when it is occupied demand is very low

Well that's strange.

What colour is this cylinder, and how much are your electricity bills? They can't be anywhere near the price of an unvented heater, surely? How much of the bill is for electricity, and how much is for standing charges? Your electricity bill will tell you what tariff you're on.

If the cylinder is properly insulated it should not lose much heat.

Why don't you just turn it off while the flat is unoccupied?

Is the immersion heater in the top of the cylinder, or near the bottom?

 

[EFLImpudence]

Aren't you planning on swapping the wrong part?

A new cylinder won't alter what is happening.

 

[stillp]

If I were to plug in the new Ariston heater into the same socket as the existing Immersion heater is run off (both are 3kW, 13A)

The immersion heater is plugged into a socket?

 

[Callum M]

John D, the cylinder insulation is a crusty browny/yellow colour and the heater is in the bottom of the cylinder.
Standing charge is 26 p, My Night charge 7 p (£40 per month) and my Day charge 15p (£160 per month), I have electric heating. This is based on Scottish winter time bills as I've only just had my first bill! The flat is let out on the holiday let market, so I can't really turn off the hot water between guests as I live remotely. I just want to avoid having a large cylinder being heated all the time between guests when there's nobody home, all for the sake of 2 x basins.

EFLImpudence, I'm removing the cylinder entirely and doing away with the gravity fed vented system. The Ariston Europrisma is a small un-vented type (mains pressure) with a small 15 litre tank which I believe would be much better suited to the low demand (2 hand basins) I have. It will cost about £180.

 

[Callum M]

STILLP - yes it's just a socket (it was like that when I bought the place). Is this a particular concern?
My thinking is that irons, kettles etc. etc. are high powered / current appliances and use sockets, is that any different? It's not in danger of being unplugged.

 

[stillp]

Is that socket on a ring final?

 

[Callum M]

Is that socket on a ring final?

Pass. I don't know. I never had problems with the existing heater tripping the RCD in the fusebox, so assumed given the comparable power rating and current draw of the old and new water heaters, it would be fine.
To find out if it's on a ring final, presumably I could plug in lights to all sockets and trip all the RCDs and by a process of elimination determine what other sockets run off the same ring?
Appreciate your interest

 

[JohnD]

You could ask your cleaner to turn off the cylinder after each let, and include instructions for turning the cylinder back on for each guest, or for whoever gets it ready for them. Also turn the heating thermostats down between lets.

The yellow insulation is rather an old spec, you can cut heat loss further by adding a red jacket (or even two) over the top. I have an idea that an insulated cylinder loses about 2 kWh per day, which would cost you about 14p if it is heated on the night rate. You ought to have a timer on it. Depending on size it will need up to about two hours to heat fully from cold, using about 6kWh, and, if insulated will stay hot for 24 hours.

Test the water temperature. If the thermostat has failed or is wrongly set it will overheat, which is expensive as well as potentially dangerous.

You say you are paying for 571kWh (£40 divided by 7p) offpeak in a month, and 1066kWh (£160 divided by 15p) peak, which seems a lot, but I don't know how big the flat is, how many heaters you have, and what temperature you heat it to, and for how many days in a month.

 

[stillp]

I never had problems with the existing heater tripping the RCD in the fusebox, so assumed given the comparable power rating and current draw of the old and new water heaters, it would be fine

It wouldn't trip the RCD unless it had an earth fault. It wouldn't trip an MCB unless it drew more current than the rating of the MCB. The concern is that if it is on a ring final circuit, and is near one end of that circuit, it might overheat the cable.
As a holiday let, doesn't it have do be electrically inspected at intervals?

 

[ericmark]

I have used the small under sink water heaters from memory around 7 litres and there are no baffles to stop water mixing so once you draw the first lot of water the second lot is just warm and it soon becomes cold it would not work with economy 7 system. You can get some heaters with baffles to stop the water mixing these tend to work better you get hot water then suddenly it runs out not gradually getting cooler but most of these give near boiling water not just hot water for your hands.

Larger cisterns do not mix the water as much so tend to last the day better. On the figures given it must take 6 hours a night to heat the water working on a 30 day month, that is a full cistern full of water every night that does not fall in with the two hand basins only. Either there is a hot water leak or something else is using the power at night.

I know the insulation may not be good enough but job one is fit extra thermal jackets not completely change the system. I would expect to find some fault, I remember with my daughter she had high bills and we found the cistern was by thermo-syphon heating some radiators. Swapped a motorised valve and bills dropped. Even lowering the temperature to 55ºC will help.

 

[EFLImpudence]

EFLImpudence, I'm removing the cylinder entirely and doing away with the gravity fed vented system.

Sorry, I misunderstood.

 

[Callum M]

Great.
Thanks for all the advice and suggestions.
The portable stuff is all PAT tested, and I've had a sparky look at the overall electrics when I bought the place and he didn't raise any concerns about things.
Despite denying it last week, my electricity supplier has now said that I would probably save money if I switched to the single rate, so I'll try that and insulate my tank better in the first instance and see how I go.

 

[JohnD]

watch the electricity meter at various times of day and night to see what is being used. You could fit an Owl or similar monitor if you want. The CM160 has a 30-day memory and will upload the figures to your PC for graphing and charts (they are often cheap on ebay).