Siemens RWB9 Timer Problem?

Hi.

I have my Siemens RWB9 timer set for Hot water to come on for an hour in the morning. (Summer Time)

The problem is the timer switching on the HW every night at 8pm for a number of hours. I think it's coming on again during the early hours.

What is happening?? I only have the timer set for 1 hour in the morning.

Thanks

Iain