Switching to a Economy 7 (two rate) plan - how can I arrange this with OVO?

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The neutral is a common conductor so is used for both circuits. The separate live conductors effectively become live at different times providing the switch between both. 
Neutral being low (near zero) voltage doesn’t need to be switched

Yes, the additional switched off-peak circuit feeds the needs of the storage heaters/hot water or whatever as appropriate 

The main input into the building would bring the common neutral in and that connection, wherever it is picked up will provide the ‘return’ connection for the live circuit. 
Will wait to see the result 

Aclara 5port meter now installed, see pic

However despite appearing correctly wired and having been quoted a day rate and a night rate, the storage heater circuit is not activating.

“unit rate1” display shows 7Kwh used since installation yesterday.

“unit rate2” display shows 0Kwh used despite my switching on 2 of my 3 storage heaters overnight.

I will be passing this to my complaints handler in the meantime, anybody got any suggestions?

Yes, there’s a relay which switches the off peak circuit.

We’ve seen a few where this isn’t set up properly so as Blastoise says, ask them to update it 

Best to check after 00:30 - otherwise the random offset might not have allowed the relay to close yet.

Yes, it should just be the extra circuit that switches on for that off peak time. 
As has been mentioned, things don’t switch at exactly the same time otherwise there would be a power surge locally from all those using the same system

Not silly at all - it’s a common misconception. There was a user complaining in this forum a few weeks ago that his off-peak (E7) usage was incrementing overnight even though the off-peak (heating) circuits were switched off at the consumer unit. He had difficulty understanding that his always-on stuff’s usage was being recorded on the ‘E7 meter’ and charged at the cheap rate during the night. I’m not sure he was convinced ...  

That looks like a very low off-peak rate to me, so it depends what you mean by standard. I don’t know whether those rates are shown including or excluding VAT, but single-rates these days are around 29p. I’d expect the peak rate for a dual-rate tariff to be well over 30p. Who did you bribe to get prices like that?

Do you know for sure when your peak and off-peak times are? They vary a lot around the country, 

The tariff is probably changing (or not, if you’re still not on an E7 plan) at the right time; it’s just the Load Control that’s not being switched. As Blastoise said, ask them (!) to resend the ALCS commands. 

[PS We’ve seen a couple of cases where the installing engineer did this and had confirmation that it was all OK (a green light on his dashboard), when it turned out not to be OK at all. Not only that, but the fix that the metering people then applied also had a (different) fault. This means that they should now know how to deal with this situation, although how far down the totem pole this knowledge trickles is anybody’s guess. My suggestion would be to write up your situation in detail in a text file, then contact a Support agent via webchat, paste the text into the chat and add your (timed) screenshots, with a request that the agent pass the whole lot on to the metering team. Be sure to include both the MPAN and the meter serial number (MSN) in the details. The MSN is visible on the meter itself, above the barcode above the window, starting with 21M.]

You are filling me with dread, as I will need to combine my 2 meters into one dual rate at some time too.  Much prefer it separate so you can see at a glance what the THTC reading is and the day rate on the other.

With solar and a small battery considering changing to a  smart meter, currently on standard tariff but considering changing to Economy 7. Does OVO provide this funcionality or do I have to change suppliers to get it?

I take your point. However, I am considering increasing the size of my battery and grid charging at night for use during the day in Winter, in Summer I generate enough to cover my night time usage and day time on an average sunny day.

Hi @tiredteddy , I was in a similar situation with a single rate meter and had been looking to use lower cost electricity to power various systems, especially as you mention, during the winter months. OVO will get there but I’m not sure when so I’ve recently switched to a provider who offers time of use (ToU) tariffs. 
It is important that you look at what you use during peak, not only 4-7pm but also during the morning from around 6-9 as these times can be higher, the evening significantly so at times. 
I believe that calculations suggest that you need to ensure that less than 30% of your usage will be during peak times but that will depend on which tariff you choose. E7 can work but it’s a little more tricky as some find that they need a boost in storage just before evening peak to last through the night