Economy 7 - Hot Water

[SusieT]

We've just moved into a new place which is on Economy 7. We've managed to work out how the heaters work but we are having trouble with our hot water - there is none, or very little and at funny times of day. We looked for a control panel but there is nothing in the house so we spoke to our supplier and they told us that it was an automatic setting warming the water between 12 and 7, but when we get up first thing there is no hot water, the pipes are completely cold. The other night we got hot water at 9pm but most of the time there is none. We checked the fuse and this is fine, apparently the boiler was replaced just before we moved in we've spoken to the plumber who did the job and said there could be a build up of scale in the tank - is this likely? We are using the Immersion and boiling the kettle to get hot water. Has anybody experienced any problems like this before? We've spoken to the previous owner and he seemed to think that he didn't have a problem with the water. Any advise from anyone would be greatly appriciated.