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bena
That's a conventional setup for three phase with the heating load switching controlled by the three phase relay driven by the auxiliary contact from the meter.
One of two things is happening here.
1. Either the meter timings and the ALC relay haven't been properly configured in which case the relay isn't being controlled by the meter.
Are you billed for an Economy 7/10 tariff with different peak and off-peak prices? Does your meter indeed show two different registers for peak and off-peak usage? Do your meters send readings automatically and are these shown on your bills as peak and off peak usage?
2. The phase supplying the live side of the relay isn't providing power because the fuse has blown and you are only getting two phases.
A little difficult to see from the photos but you have a single phase isolator switch which I assume feeds the rest of the house (lighting and power) and a three phase isolator that goes off to the heating system. It's not impossible that there is a fault on the old heating system that has caused a fuse to blow, but it's not the same phase that supplies power to the rest of the house. Unlikely, but it can happen.
The incorrect configuration of the auxiliary contact in the meter is the most likely scenario, and all I can offer in the way of diagnostics is the following:
Have a look on the display and see if their is an icon or legend that looks like a switch contact. During peak times the icon should show an open contact and it should only show as closed during the off-peak times. If there is no change between peak and off peak hours, then the relay isn't programmed properly.
To the left of the LCD display there are two LEDs that flash periodically when power is being drawn. During peak hours, one of these will flash. During off-peak hours, the other one should flash. If you only see one of these LEDs flash, no matter what time of day, then the meter isn't correctly configured for dual-rate tariff and will only bill at peak rate and never actuate the auxiliary contact.
I can't give you any more specifics than this as EDMI are notorious for not having any technical information for end users.
In any case, it is likely that when you try and speak to customer services, they won't have a Scooby what is going on, but my opinion is you need a meter engineer to come out and have a look as they have more of an idea than the helpdesk.