Totally confused by pulsacoil 2000 - off-peak always on?

I have recently moved in to a 2 bedroom electric only flat and am trying to get to grips with the pulsacoil 2000 which is installed but am at my wits end - I don't know if I'm misunderstanding something vital or what but I can't seem to find anything that clears things up for me.

Firstly, my pulsacoil 2000 doesn't have a timer - from the way some people talk about them online it implies these are standard, whereas other sources imply these aren't necessary, but I thought I'd check that this was the case as it might be related to my main problem. The main problem is that my 'off-peak' heater seems to heat at any point during the day. Whenever I run the hot tap, regardless of what time of day it is, the boiler will kick in and begin heating water to replenish the heat lost. I am assuming that the noise I am hearing is the heater and not the pump as a) it continues after the tap is turned off and b) it sounds like a boiling kettle, though less intense and on a larger scale. I know it's not the 'on-peak' heater as this is switched off at the wall (although this too confuses me as when I was testing every configuration trying to understand what was going on I had the 'on-peak' on whilst the 'off-peak' was off and this made no sound).

I should say that currently I'm not on E7 or E10 - I know I should switch to it but as it's more expensive during on-peak (and the boiler isn't currently sticking to 'off-peak') I'm worried that I'll switch, this issue will continue and I'll have another increase on my already very high energy bill.

So my questions are these:

1. Does my unit need a timer? Should I be worried that it doesn't - how will it know when is 'off-peak' without one?
2. Why does my 'off-peak' reheat regardless of the time of day? Surely this isn't by design, and how should I fix the issue?

Any help would be greatly appreciated, as currently I am completely baffled by the unit and I am struggling with energy costs.

Thanks

Matt