How do I get power to my aquastream aqualisa shower?

I bought my flat 3 years ago and have not yet done any work in the bathroom. The shower is an Aquastream Aqualisa and has a boost section on the dial. I have always thought the pressure was OK but, when visiting a friend, I noticed they had the same shower unit as me but when it is switched to the "boost" area of the dial, a pump kicked in and the water comes belting out. How can I tell if there is power going to this shower? Will the previous owner have hidden an on/off switch in the airing cupboard somewhere? We have a hot water tank... not sure if that makes any odds. We have stumbled across quite a few DIY disasters that the poor fella made so I wouldn't be surprised if he went out and bought this shower, and never bothered to install it correcly.... anyway, it would be great if after all this time, we discovered how to get the pump going.

Fingers crossed, London
June 2009