G .C. NO: 47- 2 670 1 Falcon 80 Question ?

I have a problem with my boiler, until about 2 weeks ago my boiler was always switched on which means i always had hot tap water but the central heating was off. To turn the central heating on i had to turn the time clock on. Now the central heating always comes on when i turn the ON/Off/Reset Switch to on. Is this just a setting with the time clock or has something gone wrong ? I have no ideas with boilers but i dont want to get ripped off.