I too have Quantum storage heaters running on an Economy 7 tariff. Of course, there are many variants of heater model and wiring arrangement, so it’s difficult to make concrete suggestions.

I suspect that your second Consumer Unit (the current name for what we used to call fusebox) is connected to the fifth terminal on your meter, which should then be configured to switch on and off according to your Economy 7 hours. But from what I can make out from the Dimplex documentation, it’s possible to have two supplies to the heater - one switched for E7, the other ‘always on’. There has to be power to the heater all the time for both the controls and for the fan that blows warm air out when you need it. This also makes it possible to ‘boost’ the heater’s output, for example if it runs out of steam in the evening when you most need it (any electricity used in this case will be charged at the peak rate). 

So, it should be possible to wire up your new heaters as you want them to be without having to replace the CU. 

I assume your present heaters are switching on and off as you expect them to; some users with newly-installed smart meters found that this wasn’t happening, meaning that OVO’s metering people had to wave a magic wand to get the system working.

A note about E7 tariffs: the way this works with OVO is that all usage in the offpeak period is charged at the cheap rate, while all other usage is charged at the higher rate. That’s why it’s a good idea to run power-hungry beasts like washing machines, tumble driers and dishwashers at night. If you can’t program appliances like this to finish their cycle before 07:00, say, just plug them into timer switches that are off all day and switch on only after the offpeak period has started. 

I suspect that you are correct about the Economy 7 and the second consumer unit but I’d need to check.

 Dimplex does need a constant supply to function fully - as do most of the other HHR units that I’ve looked at.

I’d hoped that the supply was now “smart” and switched tariffs rather than simply switching off on the Economy 7 circuit.

I suppose that the only way to check it is to test it in action.

The property was previously a rental so until we can get in there - probably a week or so - there’s no way to know if everything is functioning correctly. I’m assuming it is as the smart meter was installed in January so they would probably have needed to use the heating before summer.

Of course, I will still need to make a decision on what make of heater to get…

Most of the meters now being installed certainly switch circuits rather than just tariffs 

As BP says, it’s not a question of either or but rather both and. The tariff controls when the meter stops recording on the peak register and starts recording on the offpeak one. This happens on the dot, so to speak. The circuit switch operates on the same timetable, but there is a brief delay (a few minutes) built in to the meter to ensure that not every storage heater in town is switched on at the exact same moment, which wouldn’t be healthy for substation switchgear. 

Is that what’s called Dithering ??

So my hope that the economy 7 circuit supplying the storage heaters could do double duty and route the supply - economy 7 at night and peak supply during the day - is a non starter.

it looks as if I’m going to have to get things rewired 

Would it be possible to route power from the smart meter to the consumer unit controlling the storage heaters so that they are connected to peak during the day and economy 7 at night?
 

Yes .. there are two separate feeds one for peak and the other for off-peak but there are at the same (live) potential when on, so wiring both into whichever circuits are required (via MCBO trips) would do the job

So, if I’ve finally got my head straight; 

I can connect the HHR radiators to the existing economy 7 points but I will also need a separate supply going to each one to power them during the day?

Yes and as Firedog mentioned, that’s often the way they’re wired to enable both a boost circuit and the fan during the day

I’m not sure whether it’s called that, but it is a dithering mechanism - introducing a random factor to ensure that a lot of events that would otherwise happen at exactly the same time or in the same place don’t. 

Some do call it dithering although the term was meant to be used to prevent a communication overload … from the smartme.Co.Uk site

So, if I’ve got this right the system is now configured to simply switch tariffs at the appropriate time?

all consumption between midnight and 07:00 (?) being charged at the lower rate regardless of circuit?

The timings vary across the nations and regions, because they’re set by the DNO. You should be able to see the ones that apply to you on your Plan page (near the bottom).