My electricity supply is Economy 7. I have a traditional electrically-heat ed water system in my residence : a free-surface cold-water tank filled thr ough a ball-c*ck valve, and lower down a closed hot-water rank, insulated, with two immersion heaters. The lower heater is connected to the night-onl y supply, and is locally switched on permanently. The upper heater is conn ected to the 24-h supply, and is locally switched off (except sometimes). All of that is understood, and good.
A friend had the same, but did not know how to use it - that mattered littl e, since the electricity supply there had been converted to key-operated wi th no cheap night rate. To repair a leak, location unknown, the landlord h as had a new system fitted with a single closed tank using only one supply cable (the other is coiled up with the end taped over). The distribution p ipes within the residence were given some attention by the installer.
The electricity supply will, after belated digital extraction by, or supers ession of, the existing supplier, be converted to Economy 7 or similar.
What do we need to know, find, or ask?