A combi boiler will make hot water when a hot tap is turned on - there is no storage tank. You should be able to disable the heating function by using the timer/programmer or failing that by turning the Room Stat (Thermostat mounted on the wall - often in a hallway) down - 10º C perhaps.
The Worcester Bosch web site offers manuals for current and discontinued boilers - you will need the Model type.
Good luck...
Peccavi
November 2009