Why does my Ferroli F24 keep going to "boiler lock out"?

I have a three year old Ferroli F24 gas combination boiler. At some stage of most days the boiler lockout (shutdown warning) light comes on. This happens whether the heating is on permanent or timer. Using the reset button once will sometimes work but other times I have to reset it a couple of times and switch the hot water tap on at the same time so that the pilot light ignites.
This problem has only occured since using the heating system aswell as the hot water system.
For example, the heating was on timer last night and went off at 21:00hrs, it was then due to come on at 07:00hrs this morning but did not as once again the burner lockout light was illuminated.
The boiler is situated on the 1st floor of our house. Could the wind be blowing the pilot light out although I didn't have this problem last year.
Can anybody help?