not enough hot water

I am renting a flat together with a friend. The problems is that the hot water generated is enough for a 15-min shower once per day. The boiler is set to work 1am-6am, so I thought that this would be enough to have hot water during the whole day. When I press the boost, it takes hours until enough hot water has been generated. Unfortunately the letting agent don't seem to know how exactly the PulsaCoil Class A works.
The tank above the boiler is full and there are no flashing lights/other fault indicators.
I'd appreciate any help/suggestions.. thank you!

I also have a similar issue. The boiler is hot, the pipes coming out of the right of the cold fill tank are hot and there are no error lights. But a shower in the morning never really gets hot or takes a very long time to heat up. Any ideas. I have the timer set from 4-7am, does it need longer?

Many thanks.

Yes it needs longer.
Why?
It's a thermal store!
Mike
MGC/H2O
Norfolk