I have a Vailant Turbo max Boiler that wont tun off???

Can anyone help me.

I have got a Valiant Turbo Max boiler that keeps comming on during the night and warming up the radiators. We have a thermastat programe and it shoul only come on at 7 till 8 in a morning and 6 till 8 at night but i have been waking up at 2 3 4 in the morning to find the radiators are warm, not has hot as when the heating is on but im sure that once the heating turns off at 8pm the rad's should be cold till next morning and not re heat to warm durning the night?

Has anyone had this experience and if so can you let me know what you replaced on your boiler?

Thank you