worcester greenstar he boiler?

why, when I switch all the radiators, underfloor heating and hot water off at the control unit, does my boiler click on and off intermittently and use gas. I use lpg and the bills are terrible so I thought I could lower them by just using the boiler to heat the water for an hour a day. The bills are still high. I then discovered the boiler switches on itself an uses gas. Is this normal?