Hi Guys. I fitted one of these eco storage heaters the other day that needs 2 supplies. The customer was surprised when i told her as the one she had fitted a year or so ago didn't have 2 supplies although the installer had to go back several times as her rcd kept going out. I had a look at what he had done and he has basically switched the supply to on peak and i presume relying on the built in timer on the heater to switch it on and off. If this is an option then why bother having 2 supplies ? He has basically linked the 2 sets of terminals inside. I am going back there tomorrow to change it for her so that is connected as per manufacturers instructions but am wondering if it's actually necessary, i think it is but don't actually know how it is supposed to work internally.
As you say it depends on how the heater is setup internally - if there is an internal timer and it's setup correctly it could mostly work. Using a timer isn't ideal though as it can drift from the supplier's timer and in the case of smart meters, there's likely to be much more dynamic timings for “off peak” in the future.
Hopefully soon we'll have a means for equipment like this to listen to a smart meter's wireless “house area network” (the thing that supplies data to the portable in-home display) and be able to work out the cheapest time to work by itself without any special off-peak wiring at all.